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COPYRIGHT DEPOSm 



ill 



WORKS OF 

PROF. IRA O. BAKER 

PUBLISHED BY 

JOHN WILEY & SONS, Inc. 



A Treatise on Masonfy Construction. 

Materials and Methods of Testing Strength, 
etc.; Combinations of Materials— Composi- 
tion, etc.; Foundations— Bearing Power of 
Soils, etc.; Masonry Structure— Dams, Re- 
taining Walls, Abutments, Piers, Culverts, 
Vousoir Arches, Elastic Arches. Tenth Edi- 
tion, Re-written and Enlarged. 8vo, 745 
pages, 244 figures, cloth, $5.00. 

Engineers' Surveying Instruments. 

Their Construction, Adjustment and Use. 
Second Edition, Revised and Greatly En- 
larged, 12mo, ix+391 pages, 86 figures, 
cloth, $3.00. 

A Treatise on Roads and Pavements. 

8vo, xi-l-667 pages, 235 figures, 80 tables, 
cloth, $5.00. 



A TREATISE 



ON 



ROADS AND PAVEMENTS 



BY 

IRA OSBORN BAKER, C.E., D. Eng'g 

Professor of Civil Engineering, TJnimrsity of Illinois; Author of Masonry 
Construction, Engineer's Surveying Instruments; Member of 
American Society of Civil Engineers, Western 
Society of Engineers, Society for Promo- 
tion of Engineering Education 



THIRD EDITION 

RE-WRITTEN AND ENLARGED 

FIRST IMPRESSION 



NEW YORK 

JOHN WILEY & SONS, Inc, 

London; CHAPMAN & HALL, Limited 

1918 



Copyrighted 1903, 1913, 1918, 

BY 

IRA OSBORN BAKER 



MAR 29 1918 



, PRE88 OP 

BRAUNWORTH & CO. 

BOOK MANUFACTURERS 

BROOKLYN. N. Y. 



©CU494370 



'>. 




PREFACE 

FIRST EDITION 



NsT The object of this book is to give a discussion from the point of 

view of an engineer of the principles involved in the construction of 
country roads and of city pavements. The attempt has been made 
to show that the science of road making and maintenance is based 
upon well-established elementary principles, and that the art depends 
upon correct reasoning from the principles rather than in attempting 
to follow rules or methods of construction. In some cases prac- 
tical experience has not yet determined the best method of pro- 
cedure, and in these cases the conflicting views with the reasons for 
each are fully stated. 

Considerable space has been given to the economics and location 
of country roads and to the construction and maintenance of earth 
roads, since such roads constitute more than ninety-five per cent of 
the mileage of the public highways and are greatly in need of careful 
consideration. It is frequently claimed by engineers that the pubhc 
would be benefited by placing the care of the roads in the hands of 
engineers; but there is no evidence that any considerable number of 
engineers comprehend either the principles of road making necessary 
for the improvement and maintenance of our country roads, or the 
economic limitations and political d fficulties of the problem. The 
first five chapters of this book are offered as a contribution to this 
phase of the good-road problem. 

The remainder of the book, the portion that considers roads 
having permanently hard surfaces, which may not unfittingly be 
said to relate to urban and suburban roads, is based chiefly upon 
American experience, because the principles of road making worked 
out in this country are probably best suited to American conditions, 
and also because in most particulars American roads and pave- 
ments are superior to any other in the world. Some countries 
have more hard roads than this, because of a difference in condi- 
tions; but in no country does the quality of such roads average 



IV PREFACE — FIRST EDITION 



better than in this. In some foreign cities the pavements seem to 
be better cared for than in this country, owing chiefly to different 
controlUng conditions; but the principles of construction employed 
here are equal to the best. Notwithstanding the general excellence 
of the best American practice in constructing hard roads and pave- 
ments, there is still room for improvement in adapting the particular 
form of construction to the local conditions and also in preserving 
the surface from ruthless destruction. These two phases of the 
subject have been emphasized in the proper places in this volume. 
Throughout the attempt has been to state fully and clearly the 
fundamental principles of the construction and maintenance of roads 
and pavements. 

In the preparation of the book the endeavor has been to observe 
a logical order and a due proportion between the different parts; 
and great care has been taken in classifying and arranging the matter. 
It will be helpful to the reader to notice that the volume is divided 
successively into parts, chapters, articles, sections having small- 
capital black-face side-heads, sections having lower-case black-face 
side-heads, sections having lower-case itahc side-heads, and sections 
having simply the serial number. In some cases the major subdi- 
visions of the sections are indicated by small numerals. The con- 
stant aim has been to present the subject clearly and concisely. 

Every precaution has been taken to present the work in a form 
for convenient practical use and ready reference. Numerous cross 
references are given by section number; and whenever a table or a 
figure is mentioned, the citation is accompanied by the number of 
the page on which it may be found. The table of contents shows 
the general scope of the book; the running title assists in finding 
the different parts; and a very full analytical index makes every- 
thing in the book easy of access. 

The author will esteem it n favor if any errors that may be found 
are at once brought to his notice. 

I. O. B. 
Champaign, III., 
November 27, 1902. 



PREFACE 

THIRD EDITION 



The numerous changes in methods of road and pavement con- 
struction have made necessary a radical revision of this volume. 
Five years ago, before many of the changes had become well estab- 
hshed, a second edition was issued containing a supplementary 
chapter which briefly treated some of the new forms of construction. 
The present edition has been thoroughly revised and entirely re- 
written. Five chapters of minor importance have been dropped to 
make room for an equal number of new ones. The number of illus- 
trations has been greatly increased. No pains have been spared to 
bring the book up to date and to fully present the best modern 
practice. 

Attention has been given to materials and forms of construction 
that affect the quality and cost of the road and pavement, rather 
than to the machines employed and the methods of doing the work. 
In other words, the book is intended more for the one who designs 
and inspects the road or pavement than for the contractor who 
constructs it. In recent years there have been developed a number 
of machines for doing road work and for handling road-building and 
paving materials that have greatly reduced the cost of road and 
pavement construction; but to have included an adequate discussion 
of such appliances and of modern methods of operation and organi- 
zation would have greatly increased the size of the book. 

Photographs from which illustrations have been made were 
obtained from the following: 

Austin Manufacturing Co., Chicago, 111. 

Baker Manufacturing Co., Springfield, 111. 

Barber Asphalt Paving Co., Philadelphia, Pa. 

Barrett Manufacturing Co., New York City, N. Y. 

Cressy Contracting Co., Boston, Mass. 

Granite Paving Block Manufacturing Association of the U. S., Boston, Mass, 

Illinois Paving Brick Publicity Bureau, Chicago, 111. 

Illinois State Highway Department, Springfield, 111. 



VI PREFACE THIRD EDITION 



Metropolitan Paving Brick Co., Canton, Ohio. 

National Paving Brick Manufacturers Association, Cleveland, O. 

Portland Cement Association, Chicago, 111. 

Standard Oil Co., New York City, N. Y. 

U. S. Office of Public Roads and Rural Engineering, Washington, D. C. 

Mr. Walter Buehler, Chicago, 111. 

Mr. John S. Crandell, New York City, N. Y. 

Mr. Harlan H. Edwards, Danville, 111. 

Mr. Richard H. Gillespie, Chief Engineer of Streets, Bronx, New York City. 

Dr. Herman von Schrenk, St. Louis, Mo. 

The following persons have generously given valuable suggestions 
on the subject stated. 

Mr. Arthur N. Johnson, Chicago, Concrete Roads. 
Mr. Walter Buehler, Chicago, Wood-block Pavements. 
Mr. Philip P. Sharpies, New York City, Bituminous Materials. 
Mr. John W. Stipes, Champaign, 111., many matters. 
Mr. D. T. Pierce, Philadelphia, Sheet Asphalt Pavements. 
Mr. W. C. Perkins, Conneaut, Ohio, Brick Pavements. 

Mr. George N. Norton, Buffalo, N. Y., Cost of Maintenance of Sheet- Asphalt 
Pavements. 

Mr. Walter L. Weeden, Boston, Granite Block Pavements. 

Valuable data were received from many, which are specifically 
acknowledged in the text. 

To all of these the author gratefully acknowledges his obUgations. 

I. 0. B. 

Urbana, Illinois, 
January 8, 1918. 



TABLE OF CONTENTS 



PART I. COUNTRY ROADS 

Page 

Introduction 1 

CHAPTER I. ROAD ECONOMICS AND ROAD ADMINISTRATION 

Art. 1. Road Economics. Advantages of Good Roads. Cost of 
Wagon Transportation. Financial Value of Road Improvements. Tractive 
Resistance. Power of Horse. Travel Census. Weight and Width of 
Vehicles 3 

Art. 2. Road Administration. Administrative Unit. State Aid. 
National Aid. Classification of Roads. Road Taxes 31 

CHAPTER 11. ROAD LOCATION 

Elements Involved. Distance. Grade. Rise and Fall. Curves. 
Width. Cross Section. Placing the Line. Establishing Grade. Example 
of Re-location 41 

CHAPTER III. EARTH ROADS 

Art. 1. Construction. Width. Cross Section. Grades. Drainage. 
Excavation and Embankment. Improving Old Roads. Road Building 
Machinery. Cost of Earthwork. Bridges. Waterways. Culverts. Retain- 
ing Walls. Guard Rails. Guide Posts. Artistic Treatment 70 

Art. 2. Maintenance. Destructive Agents. Care of Surface: Road 
Drags and Rules for Using; Scraping Grader and Rules for Using; VRoad- 
Leveler. Care of Side Ditches. Care of Roadside. Obstruction by Snow. 
Systems of Maintenance. Expenditures for Maintenance 115 

Art. 3. Surface Oiling. Preventing Dust. Effect of Oiling on 
Maintenance. Preparing Surface. The Oil. Applying the Oil. Cost .... 133 

CHAPTER IV. SAND AND SAND-CLAY ROADS , 

Art. 1. Sand Roads. Drainage. Grading. Shade. Hardening the 
Surface 139 

Art. 2. Sand-clay Roads. The Design. Natural Mixture of Sand 
and Clay. Sand on Clay Subgrade. Clay on Sand Subgrade. Cost. 

Maintenance 140 

vii 



Vlll CONTENTS 



CHAPTER V. GRAVEL ROADS 

PAGE 

Art. 1. The Gravel. Requisites for Road Gravel. Distribution of 
Gravel. Characteristics of Different Gravels 150 

Art. 2. Construction. Drainage. Width. Maximum Grade. Crown. 
Forms of Construction: Surface Construction; Trench Construction. 
Bottom Course. Screening the Gravel. Hauling the Gravel. Measuring 
the Gravel. Cost. Economic Value of Gravel Surface. Specifications. . . . 165 

Art. 3. Maintenance. Destructive Agents. Method of Maintenance. 
Cost 178 

Art. 4. Dust Palliatives. Dust Preventives: Fresh Water, Sea 
Water, Deliquescent Salts, Proprietary Compounds, Sprinkling with Oil. . . . 181 

CHAPTER VI. WATER-BOUND MACADAM ROADS 

History 185 

Art. 1. The Stone. Requisites for Road Stone. Methods of Testing 
Stone 186 

Art. 2. Construction. Forms of Construction. Width. Crown. 
Thickness. Cross Section. Permissible Grades. Preparing Subgrade. 
Crushing the Stone. Spreading the Stone. Road Rollers. Rolling the 
Stone. Binding the Stone. Cost of Construction. Specifications 189 

Art. 3. Maintenance. Leveling. Ruts. Patching. Rolling. Sprink- 
ling. Cost 223 

CHAPTER VII. PORTLAND-CEMENT CONCRETE ROADS 

Definitions. History 227 

Art. 1. The Materials. Cement. Fine Aggregate. Coarse Aggre- 
gate. Theory of Proportions. Methods of Proportioning. Data for 
Estimates 227 

Art. 2. The Construction. Drainage. Preparing the Subgrade. 
One- vs. Two-course Pavements. Cross Section. Maximum Grade. 
Width. Thickness. Crown. Side-forms. The Concrete: proportions, 
mixing, consistency, placing, striking, finishing, curing, protecting. Con- 
traction Joints. Reinforcement. Shoulders. Curbs. Cost of Concrete 
Roads. Characteristics of Concrete Roads. Concrete Street Pavements. . 238 

Art. 3. Maintenance. Character of Work Required. Cost of Main- 
tenance 264 

CHAPTER VIII. BITUMINOUS ROAD MATERIALS 

Definitions 267 

Art. 1. Asphalt. Definitions. Characteristics of Asphalt. Sources 
of Asphalt. Specifications for Asphalt: for Bituminous Surfaces, Binder for 
Bituminous Macadam, Binder for Bituminous Coiicrete, Sheet Asphalt, 

Filler for Block Asphalt. Cost 267 

Art. 2. Petroleum. Classification. Methods of Refining. Ship- 
ping. Asphaltic Content of Road Oils. Specifications for Oil: for Park 
Drives, Earth Roads, Gravel Roads, Macadam Roads. Cost 283 



CONTENTS IX 

PAGE 

Art. 3. Tar. Definitions. Characteristics of Tar. Specifications: 
for Bituminous Surface, Bituminous Macadam, Bituminous Concrete, Joint 
Filler for Block Pavements. Cost 289 

CHAPTER IX. BITUMINOUS SURFACES FOR ROADS 

Kinds of Bituminous Surfaces 296 

Art. 1. Protective Coating. Bituminous Material 297 

Art. 2. Bituminous Carpets. Bituminous Material. Cleaning Road 

Surface. Applying Bituminous Material. Value of Bituminous Carpets. 

Maintenance. Cost 298 

i 

CHAPTER X. BITUMINOUS MACADAM AND BITUMINOUS CON- 
CRETE ROADS 

Art. 1. Bituminous Macadam Roads. Foundation. Maximum Grade. 
Crown. Wearing Course. Bituminous Binder. Tar-sand Macadam. Char- 
acteristics of Bituminous Macadam. Costs. Maintenance 306 

Art. 2. Bituminous Concrete Roads. The Aggregate. The Binder. 
Mixing. Laying. Seal Coat. Cost. Comparison of Bituminous Mac- 
adam and Bituminous Concrete 312 



PART II. STREET PAVEMENTS 

CHAPTER XI. PAVEMENT ECONOMICS AND PAVEMENT 
ADMINISTRATION 

Art. 1. Pavement Economics. Benefits of Pavements. Investment 
in Pavements 318 

Art. 2. Pavement Administration. Importance of Problem. Ap- 
portionment of Cost. Special Assessments. Guaranteeing Pavements. 
Tearing Up Pavements 321 

CHAPTER XII. STREET DESIGN 

Street Plan: checkerboard, diagonal, concentric. Size of Lots and 
Blocks. Width of Streets. Area of Stree^ts. Width of Pavement. Street 
Grades. Crown of Pavement. Cross Se(;tions of Side-hiU Streets. Plans 
and Specifications. Street Trees 336 

CHAPTER XIII. STREET DRAINAGE 

Underdrainage. Catch Basins. Gutters. Drainage at Street Inter- 
section. Surface Drainage. Crown, Rules for 361 

CHAPTER XIV. CURBS AND GUTTERS 

Curb: Stone, Concrete, Combined Concrete Curb and Gutter. Radius 
of Curb at Street Corner. Combined Curb and Walk 378 



CONTENTS 



CHAPTER XV. PAVEMENT FOUNDATIONS 

PAGE 

Art. 1. Preparation of Subgrade. Drainage. Rolling the Sub- 
grade. Filling Trenches 392 

Art. 2. The Foundation. Portland-Cement Concrete: Thickness, 
Proportions, Mixing and Placing, Finishing, Curing. Cost. Old Macadam. 
Bituminous Concrete Foundation 399 

Art. 3. Foundations for Street-railway Tracks. Foundation. 
Ties. Rails. Paving 407 



CHAPTER XVI. ASPHALT PAVEMENTS 

Art. 1. Sheet Asphalt Pavements. Classification. History. Foun- 
dation: portland-cement concrete, bituminous concrete, other forms. Binder 
Course: open, closed; cement; bitumen in binder; mixing; laying; thick- 
ness. Wearing Coat: sand; filler; cement; bitumen in wearing coat ; mixing; 
laying; rolling; thickness. Asphalt Adjacent to Tracks. Causes of Fail- 
ure. Methods of Repairing. Cost of Construction. Cost of Mainte- 
nance. Maximum Grade. Crown. Merits and Defects. Specifica- 
tions 411 

Art. 2. Asphalt Concrete Pavements. Definitions: Bitulithic, 
Warrenite, Amiesite, Topeka mixture, stone-filled sheet-asphalt, asphalt- 
concrete pavement. Mixing and Laying. Cost. Merits and Defects. 
Specifications 461 

Art. 3. Rock Asphalt Pavements. Construction 469 

Art. 4. Asphalt Block Pavements. The Blocks. Cost. Merits and 
Defects 470 



CHAPTER XVII. BRICK PAVEMENTS 

Art. 1. The Brick. The Clay. Manufacture of the Brick. Kinds 
of Brick. Size. Testing the Brick. Service Tests 474 

Art. 2. Construction. Foundation. Bedding Course* sand 
cement-sand, mortar. Laying the Brick. Joint Filler: sand, hydraulic 
grout, bituminous cement, tar-sand. Expansion Joints. Comparisor of 
Types. Brick Adjacent to Track. Maximum Grade. Brick Streets. 
Brick Roads. Cost. Merits and Defects. Specifications 503 

Art. 3. Maintenance. Repairs: soft brick, shrinkage of sand cush- 
ion, settlement of foundation, settlement of trench, defective grouting, 
bulges, re-laying pavement, cracks. Re-surfacing: asphalt top, tar top, 
turning the brick, monolithic brick top. Cost of maintenance 552 



CHAPTER XVIII. STONE-BLOCK PAVEMENTS 

Nomenclature : Roman roads, cobble-stone, Belgian-block, oblong-block, 
durax pavements 566 

Art. 1. The Stone: granite, Medina sandstone, Potsdam sandstone, 
Sioux Falls quartzite. Kettle River sandstone, limestone 569 



CONTENTS XI 



PACE 

Art. 2. Construction. Foundation. Bedding Course: sand, mortar. 
The Blocks: dressing, re-cutting, size, measuring. Setting. Ramming. 
Filling Joints. Expansion Joints. Paving Adjacent to Track. Maximum 
Grade. Merits and Defects. Durax Pavement. Cost : the blocks, granite- 
block, Medina-sandstone block, and durax pavements 572 

Art. 3. Maintenance. Re-laying. Re-filHng Joints. Spalling Joints. 
Raising Low Blocks. Settlement of Foundation. Settlement of Trench. . . . 597 



CHAPTER XIX. WOOD-BLOCK PAVEMENTS 

Kinds of Wood-block Pavements. History 601 

Art. 1 . Materials and Treatment. The Timber. Causes of Decay. 
Preservative. Treatment 603 

Art. 2. Construction. Bedding Course: sand, cement-sand, mor- 
tar, bituminous cement. Laying the Blocks. Joint Filler: sand, tar pitch. 
Open-joint Construction. Expansion Joints. Cost. Merits and Defects. 
Specifications 612 

Art. 3. Maintenance. Removing Poor Blocks. Raising Low Spots. 
Re-laying over Trenches. Lowering Bulges. Bleeding. Cost of Main- 
tenance 628 



CHAPTER XX. SELECTING THE BEST PAVEMENT 

Kinds of Pavements 633 

Art. 1. The Data for the Problem. Durability. Requirements of 
the Ideal Pavement: cost of construction, cost of maintenance, tractive 
resistance, slipperiness, ease of cleaning, noiselessness, healthfulness, freedom 

from dust and mud, temperature 635 

Art. 2. The Solution of the Problem. Economic Solution. Non- 
economic Solution , 651 



ROADS AND PAVEMENTS 



INTRODUCTION 

The problems involved in the construction and maintenance 
of rural highways differ materially from those which are encountered 
in the improvement and care of city streets, and therefore this 
discussion of the subject of Roads and Pavements will be divided 
into Part I, Country Roads, and Part II, City Pavements. In 
each division of the subject certain general principles will first be 
considered, and the further discussion will be divided according 
to the several materials in use for road surfaces. It will not always 
be possible to keep the several portions entirely distinct, but a 
knowledge of the intention in this respect will make it easier to 
understand the method of presentation or to turn readily to the 
discussion of any particular phase of the subject. 

The classification of road surfaces into country Roads and 
City Pavements is partly according to the most general use of 
each, and partly according to the elaborateness of the construction. 
According to the somewhat loose classification here adopted road 
surfaces for country roads consist of two parts, subgrade and 
wearing coat; while city pavements consist of four parts, sub- 
grade, foundation, a binder or cushion course, and a wearing coat. 

1 



PART I 
COUNTRY ROADS 

Part I will include matters relating to earth, sand and sand- 
clay, gravel, water-bound macadam, bituminous macadam, and 
concrete roads in rural districts, although some of the discussion 
is also applicable to these road surfaces when employed in city 
streets. 



CHAPTER I 
ROAD ECONOMICS AND ROAD ADMINISTRATION 

Art. 1. Road Economics 

1. Advantages of Good Roads. Good roads are so im- 
portant to the financial, social and educational well-being of a rural 
community that no enumeration of their advantages is likely to 
include all the benefits; but a brief consideration of some of the 
chief advantages of good roads will be of value in determining the 
amount of money that may justifiably be expended to secure road 
improvement and in deciding who should in equity bear this ex- 
pense. The principal advantages of good roads, i. e., of permanently 
hard ones, are as follows : 

1. Good roads decrease the cost of transportation, — at some 
seasons of the year considerably, but at others very little. This 
item will be considered more fully later (see § 4-9). 

2. Good roads make the marketing of crops easier. This ad- 
vantage results in extending the area devoted to the cultivation 
of fruits and vegetables, and is most effective in the vicinity of 
a large city. 

3. Good roads give a wider choice of time for the marketing of 
crops. In some instances good roads permit the marketing of crops 
when the labor of production is not pressing; but this advantage 

3 



4 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

accrues only to the producers of imperishable crops, and is not 
of great importance since the labor required to market the product 
is small in comparison with that of production. 

4. Good roads permit the marketing to be done when prices 
are most favorable. This advantage is more important with per- 
ishable than with imperishable products. As far as perishable prod- 
ucts are concerned, this advantage is virtually included in par- 
agraph 2 above. As far as imperishable products are concerned, 
this advantage is important only near a large city, i. e., where the 
producer hauls to the market. Prices of staple farm products (not 
garden products) are not much affected by roads, since the con- 
dition of the roads is local while prices are governed by world-wide 
conditions. Writers on good-road economics usually greatly over- 
estimate this advantage as far as the ordinary producer of imper- 
ishable products is concerned. If this advantage were anything 
like as great as is frequently claimed, producers would store such 
products at the local shipping point, or in the great city, or at the 
port of export, awaiting a favorable price. Such storage would 
also permit the delivery at a time when other work was least 
pressing. The expense of storage at the local shipping point is a 
small per cent of the value of the product. It is frequently, but 
erroneously, claimed that hard roads would save the Illinois farmer 
3 to 5 cents per bushel — an amount 10 to 15 times the cost of 
storage. Since producers do not so store their products, it is safe 
to assume that this advantage of good roads as a rule, is not very 
great. The present method of doing business makes this advantage 
comparatively unimportant. 

5. Good roads give a wider choice of the market place. This 
advantage affects perishable products chiefly, and for geographical 
reasons is, as a rule, not very great. 

6. Good roads tend to equahze the produce market between 
different weather conditions. In the absence of railroad transpor- 
tation and cold storage, this advantage might be of considerable 
local importance; but under ordinary conditions it is comparatively 
unimportant. 

7. Good roads tend to equahze railroad traffic between the 
different seasons of the year. Impassable wagon roads over any 
considerable area materially decrease the amount of agricultural 
products to be transported by railroads, and a return of good roads 
will for a time congest the railroad transportation facilities. The 
effect of good roads in equahzing railroad transportation is partially 



ART. 1] ROAD ECONOMICS 



neutralized by the fact that agricultural products are only one of 
many classes of commodities transported by the railroads; and 
also by the fact that most railroads transport agricultural products 
originating over a considerable area, and bad wagon roads are not 
likely to occur over all the contributory area at the same time; 
and further by the fact that the storage capacity of warehouses 
helps to equalize the traffic. 

8. Good roads tend to equalize mercantile business between 
different seasons of the year. Merchants having a considerable 
rural custom could do business more economically if the trade 
were . distributed uniformly throughout the yeal*. However, the 
succession of good and bad wagon roads is only one cause of the 
unequal distribution of rural patronage. 

9. Good roads permit more easy intercourse between the mem- 
bers of rural communities, and also between rural and urban pop- 
ulations. This is an important benefit, particularly under a demo- 
cratic form of government. 

10. Good roads facilitate the consolidation of rural schools, and 
thereby increase their economy and efficiency. This is an impor- 
tant matter to coming generations. 

11. Good roads facilitate rural mail delivery, and thereby tend to 
improve the social and intellectual condition of the rural population. 

12. Good roads sometimes change rural into suburban property. 

13. Good roads are a material factor in stimulating tourist 
travel and making rural communities attractive to vacation residents. 

2. It is customary to include the increase in the price of farming 
land as one of the benefits of good roads; but the increase in price 
of land is simply the measure of the value of all the above advan- 
tages, and hence should not be included. 

3. Notice that the first eight advantages mentioned above relate 
to the financial benefits of good roads, and the last four to the 
social benefits. In the past writers upon good-road economics have 
given much attention to the supposed financial benefit of hard roads 
and little or none to the social advantage. Any considerable ex- 
penditure for the improvement of rural highways can not be justi- 
fied on financial grounds alone (§ 12). Good roads are desirable 
for the same reason that a man buys an automobile or builds a 
fine house, i. e., because they are a comfort and a pleasure. Good 
roads should be urged principally for the same reason that good 
schools are maintained, namely, because they increase the intel- 
ligence and value of the citizen to society. 



6 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

4. COST OF Wagon transportation. The chief financial 
advantage of hard roads is the decreased cost of transportation. 
It is proposed to inquire briefly concerning the cost of wagon trans- 
portation with a view of determining the proportion of this cost 
that may be saved by road improvement. 

In this connection, a distinction must be made between the 
cost to those whose chief business is to sell transportation, and 
the cost to those to whom transportation is a mere incident of a 
business organized for some other purpose. The first class is rep- 
resented by a freighter, and the second by a farmer. The former 
maintains his teams and wagons only to transport freight, while 
the latter ordinarily keeps his teams and wagons primarily for 
general farm work of which transportation on the roads is only 
a small part. In some cases the traffic to be considered is prin- 
cipally that by freighters, but usually the chief traffic over country 
roads is that connected with agricultural operations. 

Again, consideration should be given only to haufing in which 
the load is equal to the full capacity of the team for the particular 
condition of the roads. A farmer may employ a two-horse team 
to take a bushel of potatoes to town, or a grocery wagon may make 
a trip to deliver a pound of cheese; but the partial load is entirely 
independent of the condition of the roads. 

Further, it is necessary to notice that only the rate for full loads 
should be considered. If a number of packages are carried in the 
same load for different parties, part of the charge is to cover the 
cost of collection, distribution, possible partial loads, etc.; and 
therefore only part of the charge is for transportation proper. 

5. Cost to Freighters. The cost will vary greatly with the 
conditions of the service, i. e., with the character of the road surface, 
the average grade of the road, the maximum grade, return load, etc. 

Except in rare cases, the cost per ton-mile for loads one way 
upon earth roads will not be more than 25 cents, and ordinarily it 
will not be more than 15 to 20 cents;* while with easy grades and 
favorable road surface it may be as low as 10 to 15 cents, and with 
long hauls, return loads, and favorable road surface, it may be 8 
to 10 cents. When the last price is obtained there is little need or 
opportunity for road improvement. 

6. Cost to Farmers. In this division of the subject, a distinc- 
tion should be made between producers of perishable products and 

* See "Cost of Wagon Transportation," by the author, in Proceedings of Illinois Society 
of Engineers, Vol. 16 (1901), p. 36-44; full abstract of the same in Engineering News, Vol. 
45 (1901), p. 86. 



ART. 1] ROAD ECONOMICS 



producers of non-perishable products. The first class is represented 
by gardeners, dairymen, fruit-growers, etc.; and the second, by 
producers of hay, grain, cotton, etc. 

The cost of transportation is much greater for perishable than 
for non-perishable products. In the first place, the marketing of 
perishable products is an important factor in comparison with 
the cost of production, and frequently necessitates an independent 
transportation department; while the labor of marketing non- 
perishable products is comparatively small — particularly as in most 
localities where there is much of this class of produce, the distance 
from the farm to the railroad station is short. Further, perishable 
products must go to market whatever the condition of the roads, 
while non-perishable ones can wait for comparatively favorable 
conditions; and finally, the former frequently go to market in 
partial loads, and the second usually in full loads. Except in com- 
paratively limited districts, non-perishable products make up the 
bulk of the traffic on the country roads. According to the U. S. 
Census of 1890, the gardeners, fruit-growers, dairymen, vine-growers, 
florists, and nurserymen constitute only 1.8 per cent of the so-called 
farming class. 

7. The cost of transporting perishable products is probably 
greater than that for any other class of traffic over the country 
roads; but as it is next to impossible to secure any reliable data 
no attempt will be made to present any general conclusions. For 
several reasons, this traffic will usually justify larger expense for 
road improvement than any other. 

The cost of transportation to farmers proper, i. e., producers of 
non-perishable products, depends chiefly upon the condition of the 
road surface and upon the demands of general farm work. Loam 
or clay roads are reasonably good when dry, and are therefore at 
least passable most of the year; while sand roads are at their worst 
when dry, and are therefore in their worst condition during the 
greater part of the year. Fortunately sand roads are less common, 
the country over, than clay or loam roads. In the crop season, 
with a little choice as to the time of doing the work the cost on 
fairly level loam or clay roads is probably not more than 10 to 
12 cents per ton-mile; and when farm work is not pressing, the cost 
is not more than 8 to 10 cents per ton-mile.* 

* See " Cost of Wagon Transportation," by the author, in Proceedings of Illinois Society 
of Engineers, Vol. 16 (1901), p. 36-44; full abstiact of the same in Engineeiing News, Vol. 
45 (1901), p. 86. 



8 



ROAD ECONOMICS AND ROAD ADMINISTRATION 



CHAP. I 



8. A Conflicting View. In current literature on road economics, 
the claim is frequently made that the cost of wagon transportation 
to the farmer is considerably more than stated in § 7. Apparently 
most of these claims are ba*sed, either directly or indirectly, upon 
data published in Circular 19 of the Road Inquiry Office of the 
United States Department of Agriculture under date of April 4, 
1896. Table 1 is a brief summary from that circular^ 

The conclusions of this circular halve been so widely quoted and 
so generally accepted as to justify a brief consideration. In former 
editions of this book, these conclusions were somewhat carefully 
considered, and the following is a brief summary of that investigation. 



TABLE 1 
Alleqed Cost op Wagon Transportation 



Ref. 

No. 


Locality. 


Average 

Distance 

Hauled, 

Miles. 


Average 
Load 

Hauled, 
Tons. 


Average 

Coi?t per 

Ton-mile, 

Cents. 


Total Cost 

from Farm 

to Market, 

per Ton. 


1 


Eastern States. 


5.9 

6.9 
8.8 

12.6 
8.8 

23.3 


1.108 

'o:688' 
1.204 
1.098 


32 

27 
31 
25 

22 
22 


$1 89 


9 


Northern States 


1 86 


3 

4 


Middle-Southern States 

Cotton States 


2.72 
3.05 


5 


Prairie States. 


1 94 


6 


Pacific Coast and Mountain. . . . 
Whole United States 


5.12 


7 


12.1 


1.001 


25 


3.02 









Circular 19 concludes that 313,349,227 tons were hauled over 
the highways of the United States in 1895 at a cost of $3.02 per 
ton-mile, or a total cost of $946,314,665.54; and that the annual 
cost of transporting the crops of the United States to market was 
26.6 per cent of the price of the crops at the market. These con- 
clusions are greatly in error chiefly for the following reasons: 

1. The investigation was not very elaborate, since replies were 
received from only one county in thirty. 

2. The average distance hauled seems to be about twice too 
great. 

3. The value for the average load hauled is approximately 
twice too great. The mean between the maximum and the mini- 
mum load may be one ton; but the great bulk of teaming is done 
when the roads are at least in fair condition, when the load is con- 



ART. 1] ROAD ECONOMICS 9 



siderably more than one ton. The author has examined the records 
of several grain buyers in central Ilhnois, where at times the roads 
are as bad as anywhere, and finds that the average load is nearly 
a ton and a half. Statistics for marketing over 300,000 bushels 
of corn in Illinois gives the average load as almost exactly 2 
tons. 

4. The cost per ton-mile indicates that this value was obtained 
by assuming that the wages of wagon, team, and driver are 35 cents 
per hour; that the team travels 3 miles per hour; and that the 
team hauls a load only one way. The price per hour for a team 
is too great, since the cost per day as reported by 316 farmers in 
76 counties in Illinois varied during crop time from $1.40 to $2.74, 
the average being only $2.13, or say 21 cents per hour. 

5. No account was taken of the relative amounts of traffic in 
the several states. 

9. Under date of Feb. 28, 1907, the Bureau of Statistics of the 
U. S. Department of Agriculture published Bulletin 49 — Cost of 
Hauling Crops from Farm to Shipping Point. In the latter investi- 
gation the cost of hauling the twelve leading farm products from 
the farm to the shipping point during the crop year of 1905-06 
is said to be $84,684,000; whereas in the first investigation (§8), 
the cost in 1895 of hauling all crops from the farm to the market 
was said to be $652,000,000. Notice that the cost according to 
the later and more elaborate investigation is only about one eighth 
of that by the former investigation, notwithstanding the fact that 
the weight of the seven leading crops was almost exactly 50 per 
cent greater in 1905 than in 1895; in other words, on the face of 
the returns, the result in the first bulletin is about sixteen times 
too great. 

Further, the result of the second investigation is subject to 
errors 2, 3, and 4 of § 8. Besides, the second bulletin is greatly 
in error for the following reasons: It finds the cost of hauling crops 
from the farm to the market to be $72,984,000; and then adds 
$11,700,000 as the cost of hauling wheat to local mills to be ground. 
This allowance is altogether too great, since it assumes that more 
than one third of the wheat not used for seed is ground at the local 
mill; while only an inappreciable quantity is so used. 

Correcting the above errors would reduce the total of the second 
bulletin to one half or one third, and make the result in the first 
bulletin thirty to fifty times too great. Unfortunately the results 
of the first investigation are frequentl}^ used in discussions on road 



10 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. 1 

economics, and the object of this note is to show their utter unre- 
liabihty.* 

10. Possible Annual Saving. The Office of Road Inquiry, in 
Circular No. 19, to which reference has been made, estimates the 
possible annual saving by road improvement as $628,000,000. 
This estimate is based upon a comparison of the data in Circular 
No. 19 with that on the ''Cost of Hauling Farm Products to Market 
or Shipping Point in European Countries, Collected by U. S. Con- 
sular Agents,'' published in Circular No. 27 (Feb. 5, 1897) of the 
Office of Road Inquiry of the U. S. Department of Agriculture. 
The average cost as given in the latter circular is 10 cents per ton- 
mile, and the difference between this and the average stated in 
Table 1 is 15 cents per ton-mile, which is two thirds of the average 
value in Table 1. 

Concerning the data for America, notice that they are taken 
from Circular No. 19, and are greatly in error as has already been 
shown. Concerning the data for Europe, notice in the first place 
that they are open to most of the criticisms made against the data 
in Table 1. In the second place, the twelve results given in Cir- 
cular 27 vary from 4 to 30 cents per ton-mile, which is too wide a 
range and too few results for an accurate determination of the 
average cost of wagon transportation in Europe. In the third 
place, some of the results are professedly the cost to transportation 
companies, and some the cost to farmers to whom the hauling of 
the crops to market is merely an incident of farm work. And, 
finally, the data for the cost of hauHng not done by transportation 
companies are for hauling garden products, etc., to large cities, 
and are therefore not representative of the cost of transporting 
general farm products to market. 

11. It is very unfortunate that the conclusions from the two 
Circulars referred to above, have been so generally accepted by 
speakers and writers upon good-road economics. Country roads 
are used chiefly by farmers, and if improvements are made they 
must be paid for largely, if not entirely, by farmers; and therefore 
the cooperation of farmers must be secured before any improve- 
ment of the country roads is possible. Farmers know that con- 
clusions such as are deduced above from Table 1 are ridiculous; 
and not unnaturally distrust the motives prompting the argument, 

* For a further discussion of the Circular see the following: In defense of the Circular, 
Engineering News, Vol. 34, p. 410-11; do.. Vol. 45, p. 50-51. Controverting the Circular: 
Engineering News, Vol. 34, p. 377-78; do.. Vol. 34, p. 410-11; do., Vol. 44, p. 337-44; do., 
Vol 5, p. 48-49; do., Vol. 57, p. 428. 



ART. 1] ROAD ECONOMICS 11 

and are hostile to all propositions for road improvement supported 
by such arguments. 

Further, it is not possible to determine either the cost of wagon 
transportation or the financial value of road improvement in the 
wholesale manner proposed in the above Circulars. The cost of 
haul and the value of improved roads vary greatly with local con- 
ditions; and consequently a special investigation should be made 
for each particular case. 

However, it should be borne in mind in discussing road eco- 
nomics that financial profit is only one of the advantages of good 
roads (see § 1-3). 

12. FINANCIAL VALUE OF ROAD IMPROVEMENT. It is not 
possible to present any valuable general conclusions as to the saving 
in cost of transportation attainable by any proposed road improve- 
ment. 

For any particular road where the traffic is principally by 
''freighters" as defined in §5, it is possible to arrive at a rough 
approximation by (1) taking a census of the traffic, (2) making 
an estimate of the present cost per ton-mile, and (3) making an 
estimate of the cost after the improvement. The amount of traffic 
varies with the condition of the road surface, and the chief difficulty 
is to determine the advantage of being able to move freight at any 
time. This advantage will depend upon the proportion of the time 
that the roads are ''good," which depends entirely upon the local- 
ity and the nature of the road surface, and varies greatly from 
year to year. Ordinarily the road is used by a variety of team- 
sters, and the cost varies with the particular circumstances of each. 
There will rarely be conditions to which this method of investiga- 
tion can be applied with any degree of certainty. At best the 
results of such an investigation must be regarded as mere approx- 
imations, since no factor of the problem can be determined accu- 
rately, and since any sHght error in the estimated saving per 
ton-mile is greatly magnified when multiplied by the number of ton- 
miles. Nevertheless such an investigation is desirable to aid the 
judgment, but its approximate nature must not be forgotten. 

For roads where the travel is by farmers the difficulties are still 
greater. The number of users is greater, the cost of transportation 
to the different users varies very greatly, and the value of being 
able to use the road at any time is very different with different 
users, and for the same class of users varies with the locality and 
the nature of the road. 



12 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

The amount of money that may justifiably be expended for any 
proposed road improvement will depend upon the present condition 
of the road, the amount and the nature of the travel, and the cost 
of constructing and maintaining the improved road. The ques- 
tion is a local one, and can be answered approximately correctly 
only after careful study of the conditions. Ordinarily the saving 
in transportation, except near large cities, will not justify any 
radical road improvement; but with a miscellaneous travel, the 
social advantages of road improvement should be taken into con- 
sideration, even though they can not be computed in dollars and 
cents. 

13. TRACTIVE Resistance. The solution of some problems con- 
nected with road improvement requires a knowledge of the tractive 
resistance. Until recently all vehicles were horse-drawn; but now 
many are propelled by motors. The passenger automobile with 
its wide range of speed and power is able to surmount almost any 
grade hkely to be encountered upon a road used also by horse- 
drawn vehicles; and automobile trucks are not common, at least 
yet, upon rural roads, and besides the factors governing the tractive 
power of such vehicles are not yet well established. Hence the 
road problems involving tractive resistance relate almost exclu- 
sively to horse-drawn vehicles; and consequently only this class 
will be considered under this head. 

The resistance to traction of a vehicle on a road consists of three 
independent elements: axle friction, rolhng resistance, and grade 
resistance. 

14. Axle Friction. The resistance of the hub to turning on 
the axle is the same as that of a journal revolving in its bearing, 
and has nothing to do with the condition of the road surface. The 
coefficient of journal friction varies with the material of the journal 
and its bearing, and with the lubricant. It is nearly independent 
of the velocity, and according to observations made by the author 
seems to vary about inversely as the square root of the pressure. 
For light carriages when loaded, the coefficient of friction is about 
0.020 of the weight of the axle; for heavier carriages when loaded, 
it is about 0.015; and for the ordinary thimble-skein American 
wagon when loaded, it is about 0.012. The above results are for 
good lubrication; if the lubrication is deficient, the axle friction 
is two to six times as much as above. The above figures agree 
reasonably well with results obtained for journal friction of ma- 
chines. Apparently the value of this coefficient in Morin's experi- 



ART. 1] 



ROAD ECONOMICS 



13 



merits (§ 20) was 0.065.* The greater axle friction is probably 
due to the inferior mechanical construction of French carriages 
and wagons of that date. 

The tractive power required to overcome the above axle friction 
for American carriages of the usual proportions is about 3 to 3| lb. 
per ton of the weight on the axle; and for truck wagons, which 
have medium-sized wheels and axles, is about 3| to 4J lb. per ton. 

15. Rolling Resistance. The resistance of a wheel to rolling 
along on a road is due to the yielding or indentation of the^ road, 
which causes the wheel to be continually climbing an inclination. 
The resistance is measured by the horizontal force necessary at the 
axle to lift the wheel over the obstacle or to roll it up the inclined 
surface; and varies with the diameter of the wheel, the width of 
the tire, the speed, the presence or absence of springs on the vehicle, 
and the nature of the road surface. 

16. Diameter of Wheel. The rolling resistance varies inversely 
as some function of the diameter of the wheel, since the larger the 
wheel the less the force required to lift it over the obstruction or 
to roll it up the inclination due to the indentation of the surface. 
Table 2 shows the results obtained by Mr. T. I. Mairs at the Mis- 
souri Agricultural Experiment Station,* with three different-sized 



TABLE 2 

Effect of Size of Wheels on Teactive Resistance f 

Resistances in Pounds per Ton 



Ref. 

No. 


Description of Road Surface. 


Mean Diameter of Front 
AND Rear Wheels. 


50" 


38" 


26" 


1 

2 
3 


Macadam : slightly worn, clean, fair condition .... 

Gravel road: dry, sand 1" deep, some loose stones. 

Gravel road: up grade 2.2%, |" wet sand, frozen 

below 


57 

84 

123 
69 
101 
132 
173 
178 
252 


61 
90 

132 
75 
119 
145 
203 
201 
303 


70 
110 

173 


4 


Earth road: dry and hard 


79 


5 
6 

7 
8 
9 


'' " 1" sticky mud, frozen below, rough. . 

Timothy and blue-grass sod: dry, grass cut 

* * ' * ' * ' ' wet and spongj^ 

Corn-field: flat culture, across rows, dry on top. . . 
Plowed ground : not harrowed, dry and cloddy . . . 

Average value of the tractive power 


139 
179 

281 
265 
374 


10 


130 


148 


186 









* Lowe's Strassebaukunde, page 75. Wiesbaden, 1895. 

t Missouri Agricultural Experiment Station, Bulletin No. 52, Columbia, 1902. 



14 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

wheels. The 50-inch represents 44-inch front and 56-inch hind 
wheels; the 38-inch represents 36-inch front and 40-inch hind wheels; 
and the 26-inch represents 24-inch front and 28-inch hind wheels. 
The tires were 6 inches wide. The load was practically If tons 
in each case. 

Morin concluded that the resistance varies inversely as the first 
power of the diameter of the wheel; Dupuit that it varies as the 
square root; and Clarke claims that it varies as the cube root.* 
According to some experiments made in England in 1874, f the 
tractive resistance varied more rapidly than the first power of the 
diameter of the wheels. The mean results in Table 3 vary nearly 
inversely as the square root of the mean diameter — certainly more 
nearly than as either the first power or the cube root. For obvious 
reasons, the experiments can not be very exact; and apparently 
the tractive resistance varies differently for different ^surfaces. The 
exact determination of the law of variation is of no great importance. 

17. Width of Tire. If the wheel cuts into the road surface, the 
tractive resistance is thereby increased; but with surfaces for which 
there is little or no indentation, the traction is practically inde- 
pendent of the width of tire. 

Table 3, page 15, shows the results of an elaborate series of 
experiments by the Missouri Agricultural Experiment Station.! 
The load in each case was 1 ton. These results show that on poor 
macadam, poor gravel, and compressible earth roads, and also on 
agricultural land, the broad tire gives less resistance except as 
follows: (1) when the earth road is sloppy, muddy, or sticky on top 
and firm underneath; (2) when the surface is covered with a very 
loose deep dust and is hard underneath; (3) when the mud is very 
deep and so sticky that it adheres to the wheel; or (4) when the 
road has been rutted with the narrow tire. The last conclusion 
was established by a large number of experiments not included in 
Table 3. 

Table 4, page 16, gives data on the effect of width of tire upon 
the tractive power, obtained by the Studebaker Bros. Manufactur- 
ing Co., South Bend, Ind., in 1892, with an ordinary 3|-inch thimble- 
skein wagon. Notice that on a hard and incompressible road sur- 
face, e. g., wood block pavement and gravel, the narrower tire draws 



* Clarke's Construction of Roads and Streets, p. 294. London, 1890. 

t Clarke's Manual of Rules, Tables and Data for Mechanical Engineers, p. 962. London, 
1877. 

X Missouri Agricultural Experiment Station, Bulletin No. 39, Columbia, Mo., July, 1897. 



mm 



ART. 1] 



ROAD ECONOMICS 



15 



TABLE 3 

Tractive Resistance of~Broad^and Narrow Tires * 

Resistances in Pounds per Ton 



Ref. 
No. 



Description of the Road Surface. 



Width of Tire. 



U' 



No. of 
Trials. 



6 
7 
8 
9 
10 
11 

12 
13 



14 

15 
16 



17 

18 
19 



20 
21 
22 



23 

24 



Broken Stone Road: 
Hard, smooth, no dust, no loose stones, nearly 
level 

Gravel Road: 

Hard and smooth, few loose stones size of black 

walnuts 

Hard, no ruts, large quantity of sand which 

prevented packing 

New, gravel not compact, dry 

Wet, loose sand I" to 2^" deep 

Earth Roads: 

Loam, — dry, loose dust 2" to 3" deep 

' ' " hard, no dust, no ruts, nearly level. 

' * stiff mud, drying on top, spongy below . 
' ' mud 2\" deep, very sticky, firm below. 
Clay, — sloppy mud 3" to 4" deep, hard below . 
" dry on top but spongy below, narrow 

tires cut in 6" to 8" 

' * dry on top but spongy below 

' ' stiff deep mud 

Mowing Land: 

Timothy sod, — dry, firm, smooth, narrow tire 

cuts in 1" 

" " moist, narrow tire cuts in 3^". . 

" " soft and spongy, grass and 

stubble 3" high, narrow tire 

cuts in 6" 

Pasture Land: 

Blue-grass sod, — dry, firm, smooth . 

' ' " soft, narrow tire cuts in 3". . . 
" " narrow tire cuts in 4" 

Stubble Land: 

Corn stubble, — no weeds, nearly dry enough 

to plow 

" " some weeds and stalks, dry 

enough to plow 

" " in autumn, dry and firm 

Plowed Land: 

Freshly plowed, not harrowed, surface rough . . 
" " harrowed, smooth, compact. . . 



121 



182 



569 

218 
420 

578 



631 

423 
404 



510 
466 



98 



134 



239 


157 


1 


330 


260 


1 


246 


254 


2 


90 


106 


2 


149 


109 


3 


497 


307 


1 


251 


325 


1 


286 


406 


1 


472 


422 


2 


618 


464 


5 


825 


551 


1 


317 


229 


1 


421 


305 


1 



327 

156 
273 
436 



418 

362 
256 



283 
323 



* Missouri Agricultural Experiment Station, Bulletin No. 39, Columbia, Mo., July, 1897. 



16 



ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. 1 



TABLE 4 

Effect of Width of Tire upon Tractive Power * 

Resistances in Pounds per Ton 





Description of the 
Road Surface. 


Diameters of the Fhont and Rear Wheels Respectively. 


Ref. 
No 


3' 6" and 
3' 10". 


3' 6" and 
3' 10". 


3' 8" and 
4' 6". 


3' 6" and 
3' 10". 


3' 8" and 
4' 6". 




Width of the Tire. 




U" 


4" 


ir 


4" 


U" 


4" 


U" 


3" 


If" 


3" 


1 


Sod 














283 

152 


239 
152 


189 
114 
265 


228 


2 


Earth Road, hard. . . . 

" '' muddy.. 
Sand Road, hard 

" " deep .... 
Gravel Road, good . . . 


199 
371 


108 
243 
162 
351 










114 


3 


268 
171 


304 
164 


236 
141 


254 
168 


228 


4 








5 










6 


98 
61 


117 
70 


83 
35 


80 
46 






66 

28 


76 


7 


Wood Block, round . . 


51 


49 




54 


38 



the easier; while upon the soft or spongy surface the wider tire 
draws the easier. 

Morin experimented (see § 20) with tires 2i, 4§, and 6| inches 
wide; and concluded that on a soUd road or pavement the resist- 
ance was independent of the width of the tire, but on a compressible 
surface the resistance decreased as the width of the tire increased, 
the rate depending upon the nature of the surface. 

For a further discussion of the relative merits of broad and narrow 
tires, see § 200-202. 

18. Effect of Speed. The rolling resistance increases with the 
velocity, owing to the effect of the shocks or concussions produced 
by the irregularities of the road surface. This increase is less for 
vehicles having springs than for those not having them, and is also 
less for smooth road surfaces than for rough ones. 

Table 5, page 17, is a summary of Morin's results (see § 20) 
showing the effect of a variation of speed for vehicles provided 
with springs. In a rough way the three speeds are 2J, 5, and 7J 
feet per second, or about 2, 4, and 6 miles per hour respectively. 
According to these results the resistance on broken-stone roads 
increases roughly as the fourth root of the speed, and on stone-block 
pavement about as the square root. For springless vehicles the 
increase would be greater. The above is for metal tires; for pneu- 



* Pamphlet by Studebaker Bros, Manufacturing Co., South Bend, Ind., 1892. 



ART. 1] 



ROAD ECONOMICS 



17 



TABLE 5 

Effect of Speed on Tractive Power * 
The figures give the resistance in pounds per ton 



Ref. 

No. 



Description of the Road Surface. 



Broken Stone Road: 
Good condition, dry and compact 
Very firm, large stones visible. . . . 

Little moist, or little dirty 

Firm, little soft mud 

' ' ruts and much mud 

Portions worn out, thick mud. . . . 
Much worn, ruts 3" deep, thick mud 
Very bad, ruts 4" deep, very rough 

Stone Block Pavement: 

Very smooth, narrow joints 

Fair condition, dry 

Moist, covered with dirt 



Stage Coach. 



Walk, 



42 

59 

49 

77 

95 

112 

146 

164 



32 
35 
35 



Trot. 



75 
75 
92 
108 
127 
161 
180 



48 
52 
49 



Fast 
Trot. 



50 

81 
88 
100 
117 
134 
169 



55 
61 
56 



Cakriage. 



Wallc. 



41 

58 

48 

76 

93 

110 

145 

162 



31 
34 

44 



Trot. 



48 

73 
74 
91 
108 
126 
160 
202 



47 
51 
60 



Fast 
Trot. 



49 

81 

88 

99 

116 

132 

168 



54 
67 
67 



matic tires there is very little increase of resistance with increase 
of speed, t 

The preceding data refer to the effect of speed upon the tractive 
power after the load is in motion. It requires from two to six or 
eight times as much force to start a load as to keep it in motion at 
2 or 3 miles per hour. The extra force required to start a load is 
due in part to the fact that during the stop the wheel may settle 
into the road surface, in part to the fact that the axle friction at 
starting is greater than after motion has begun, and further in part 
to the fact that energy is consumed in accelerating the load. 

19. Effect of Springs. Springs decrease the tractive resistance 
by decreasing the concussions due to irregularities of the road sur- 
face, and are therefore more effective at high speeds than at low 
ones, and on rough roads than on smooth ones. Apparently no 
experiments have been made upon the effect of springs; but a few 
data on this subject may be obtained by comparing the last and the 
sixth columns of Table 6, page 18. 

20. Results of Early French Experiments. Immediately before 
and shortly after the introduction of railroads, European engineers 
made many experiments on the force necessary to draw different 
vehicles over various surfaces. The experiments by Morin,* made in 

* Experiences sur le tirage des voitures et sur les effets destructeurs qu'elles exercent siir 
les routes, executees en 1837 et 1838 par ordre du Ministre de la Guerre, et en 1839 et 1841 
par ordre du Ministre des Travaux Publics, A. Morin. Paris, 1842. 

t Proc. of Inst, of Mecb. Engrs. (London), for 1890, Part No. 2, p. 195, 



18 



ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 



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AKT. 1] 



ROAD ECONOMICS 



19 



1837-41 for the French Government, were much the most elaborate 
and appear to have been made with great care. Table 6, page 18, 
is a summary of Morin's results showing the tractive resistance for 
different vehicles on various road surfaces. The table represents 
about 700 experiments. 

21. Results of Modern American Experiments. Table 7, page 
20, shows data obtained by the author. The tractive power was 
determined with a Baldwin dynograph, Fig. 1 . The instrument con- 
sists of two long flat springs fastened together at their ends and 




TOP VIEW 




BOTTOM VIEW 
Fig. 1. — Baldwin Dynograph. 



20 



ROAD ECONOMICS AND ROAD ADMINISTRATION [cHAP. } 



having their centers slightly farther apart than their ends. One 
end of the apparatus is attached to the wagon, and the team is 
hitched to the other. The pull of the team causes the centers of the 
flat springs to approach each other. One spring supports a gradu- 
ated disk, and the other is connected to an index arm which is pivoted 
at the center of the disk. From one end of this index arm, the pull 
can be read directly from the graduated disk. There are two extra 
index arms — one to indicate the maximum power developed and one 
to indicate a rough average. The former (the upper one in Fig. 1) is 
simply pushed around by the main index arm and is left at the highest 
point. The latter (the middle arm in Fig. 1) has a transverse slot 
in which plays a stud on the main index arm. When making an 

TABLE 7 
Tractive Resistance on Level Pavements 



Expt. 
No. 



Location and Description of the Pavement. 



Pounds 
per 
Ton. 



bet. 43d and 44th Sts.; smooth, clean, 
bet. 43d and 44th Sts.; smooth, clean. 



Asphalt: Chicago — Calumet Ave., 

no cracks, 52° F 

Chicago — Calumet Ave., 

no cracks, 84° F 

Chicago — Washington BouL, bet. Halsted and Green Sts.; 

smooth, clean, no cracks, 42° F 

Brick: Champaign — University Ave., west of New St.; 3 X 9-in. brick 

on concrete, corners rounded, sand filler, not worn, clean 

Champaign — Second South St.; same as No. 4, except newer and 

covered with |-in. of dust 

Champaign — First South St.; same as No. 4, except cement filler, 

just completed 

Chicago — Peoria St., between Washington and Randolph; 2| X 8- 

in. brick on concrete, pitch filler, new 

Chicago — Laurel St. Stock Yards; 3X 8-in. brick on gravel and 

cinders, sand filler, corners not rounded 

Chicago — Exchange Ave., Stock Yards; 2f X 8-in. brick on sand 

and old macadam, tar filler, new 

Gianite block: Chicago — Exchange Ave., Stock Yards; smoothly dressed 
3 X 9-in. blocks on concrete, joints J in., tar filler, not 

worn 

Chicago — Randolph St., between Desplaines and Halsted; 
smoothly dressed blocks on concrete, pitch filler, new. . 
Chicago — Halsted St., between Randolph and Washing- 
ton; ordinary granite, 9 years old 

Macadam: Chicago — Michigan Ave., between 42d and 43d Sts.; granite 

top, no dust, no mud 

Plank road: Chicago — Packer's Ave., Stock Yards; oak plank, 3 X 12-in. 

nearly new 

Exactly same as above aifter worn down I in. in many places, 

clean • • 

Substantially same as above; covered with J-in fine loose dirt 

Steel wheelway: Chicago — Transit Ave., Stock Yards; 8-in. 11? lb. 

channel on 2 X 8-in. pine, that on macadam, covered 

with i-in. powdered stone 

Same when scraped with a shovel 

Same when covered with |-in. fine dust 

Wood block: Rectangular blocks 3 X 12-in. considerably worn 

Cylindiical cedar block covered with |-in. silica pea gravel 
Exactly same as above covered with f-in. crushed gravel. . 
Cylindrical cedar block; clean, blocks slightly convex on top 
Cylindrical cedar block on 2-in. plank and 2 in. of sand, clean, 

not worn • • • 

Same as above; clean, slightly worn 

Same as above; clean, considerably worn 



40 
19 
28 
36 
90 
50 
53 

37 
51 
54 



AKT. 1] 



ROAD ECONOMICS 



21 



experiment the main index arm is' continually in motion, and the 
position of the auxiliary arm roughly indicates the average power 
exerted. The end of the index arm opposite the graduated arc 
records the amount of tractive resistance upon a strip of paper which 
is wound from one cylinder to another by clock-work located behind 
the lower right-hand corner of the top view of Fig. 1. The auto- 
graphic record is more accurate than the indicated reading. 

The wagon employed was the usual thimble-skein four-wheel 
farm wagon with a 2-inch tire. Experiments 3, 4, and 5 were made 
with wheels averaging 42 J inches in diameter, and the remainder 
with wheels averaging 47 inches. 

22. From a study of the preceding experiments and also others 
not here described, it is concluded that the average tractive resist- 
ance on different road surfaces is about as in Table 8 which is given 
for use in comparing different roads and pavements. 

TABLE 8 
Standard Tractive Resistance of Different Roads and Pavements 



Ref. 


Kind of Road Surface. 


Tkactive Resistance. 


No. 


Pounds per Ton. 


In Terms of Load. 


1 


Asphalt — artificial sheet 


30- 70 
15- 40 
50-100 
27- 30 
50-200 
50-100 
20-100 
30- 50 
100-200 
30- 80 
15- 40 
30- 50 
40- 80 


^3^ 


2 
8 


Brick 

Cobble stones 


Tis-.[6 


4 
5 
6 


Portland cement concrete, unsurfaced 
Earth roads — ordinary conditions. . . 
Gravel roads . . 




7 


Water-bound macadam 




8 


Plank road 


-6-7— /o- 


q 


Sand — ordinary condition 


%-% 


10 


Stone block 


^vX 


n 


Steel wheelway 




12 
13 


Wood block — rectangular 

' ' cylindrical 


^7-^ 
^-^ 



23. Grade Resistance. This is the force required on a grade 
to keep the load from rolling down the 
slope. It is independent of the nature 
of the road surface, and depends only 
upon its angle of inclination. 

In Fig. 2, P is the grade resistance, 
and W is the weight of the wheel and 
its load. From the diagram it is easily seen that P = IT X B C -^ 
A C. For all ordinary cases, A C may be considered as equal to 
A B, and then P = WXBC-t-AB, 




Fig. 2. 



22 ROAD ECONOMICS AND ROAD ADMINISTRATION ^CHAP. I 

The preceding analysis is approximate for three reasons: (1) 
assuming A C = A B, i. e., assuming the sine of inclination to be 
equal to the tangent; (2) assuming the normal pressure on the 
incHned road surface to be equal to the weight, i. e., assuming the 
cosine of the inclination to be unity ; and (3) neglecting the fact that 
the hind wheels carry a greater proportion of the load on an incHna- 
tion than on the level. The resulting error, however, is wholly 
inappreciable. 

Grades are ordinarily expressed in terms of the rise or fall in feet 
per hundred feet, or as a per cent of the horizontal distance. If 
A 5 be 100 feet, then the number of feet in 5 C is the per cent of the 
grade; and therefore the grade resistance is equal to the load mul- 
tiplied by the per cent of the grade. Or the grade resistance is 
equal to 20 lb. per ton multiplied by the per cent of the grade. 

24. Power of a Horse. The horizontal pull which a horse can 
exert depends upon its weight, its build, the method of hitching, the 
foothold afforded by the surface, the speed, the length of duration of 
the effort, the rest-time between efforts, and the tax upon the future 
efficiency of the horse. The chief of these are the weight, the speed, 
and the length of the effort. 

Horses vary in weight from 800 to 1,800 lb. The larger horses 
do not usually travel more than 2^ or 3 miles per hour. With 
reasonably good footing a horse can exert a pull equal to one tenth 
of its weight at a speed of 2J miles per hour (3| feet per second) 
for 10 hours per day for 6 days per week and keep in condition. 
This is a common rate of exertion by farm horses in pulling plows, 
mowers, and other agricultural implements. On this basis a 1500- 
Ib. horse would develop 550 foot-pounds per second (the conven- 
tional horse-power), and 16,500,000 foot-pounds per day. This 
may be considered about the limit of endurance. A lighter horse wiU 
exert a proportionally less force. If the time of the effort is decreased, 
the draft may be proportionally increased ; or if the speed is increased, 
the draft must be decreased in a like proportion. In other words, the 
foot-pounds of energy that can be developed per day by any particular 
horse.is practically constant. 

The maximum draft for a horse is about half of its weight, 
although horses have been known to exert a pull of two thirds of 
their weight. Most horses can exert a tractive power equal to half 
their weight, at a slow walk for about 100 feet. On the road in 
emergencies, as in starting the load or in overcoming obstacles, a 
horse may be expected to exert a pull equal to half its weight, but 



AKT. 1] HOAD ECONOMICS 2S 

at this rate it would develop a day's energy in about 2 hours; and 
consequently if it is expected to work all day, it should not be 
called upon to exert its maximum power except for a short time. 
Similarly, a horse can exert a draft equal to one quarter of its weight 
for a longer time. The working tractive power of a horse may be 
taken as one tenth of its weight, with an ordinary maximum of one 
quarter, and in great emergencies a maximum of one half its weight.* 

25. Increasing the number of horses does not increase the power 
proportionally — for somewhat obvious reasons. It is stated that 
for a two-horse team the efficiency of each horse is about 95 per 
cent; for a three-horse team, about 85 per cent. Of course such 
data are not much more than guesses. 

26. Effect of Grade. The effective tractive power of a horse 
upon an inclined road surface is decreased by the fact that the 
horse must lift his own W3ight up the grade. If 7"= the tractive 
power, W = the weight of the horse, t = the tractive power on the 
level in terms of the weight of the horse, and g = the rise of the 
grade per unit of horizontal distance, then, with sufficient accuracy, 

T = tW - gW = (t- g)W (1) 

If it be assumed that the average working tractive power of the 
horse is one tenth of its weight, then t = 10 per cent; and equation 
(1) shows that on a 1 per cent grade the horse can exert an effective 
tractive power of 9 per cent of its weight, and also that it will be 
able to carry its own weight up a 10 per cent grade. If it be as- 
sumed that the horse exerts a tractive power equal to 20 per cent of 
its weight, then equation (1) shows that on a 10 per cent grade it 
can take its own weight up and in addition exert a tractive power of 
10 per cent of its weight upon the load. By assigning values to t 
and g, equation (1) readily shows the effective draft of a horse upon 
any grade. 

Equation (1) is not mathematically correct, since it assumes 
that the weight of the horse is always normal to the road surface. 
However, the formula is sufficiently accurate for use in comparing 
the relative tractive power of a horse on different grades (§ 27). 
At best such a formula can be only approximate, since the tractive 
power varies greatly with the foothold. 

* For the results of experiments made at the Kansas State Agricultural College, showing that, 
a horse in pulling from 500 to 1500 feet probably exerted from 2G to 42 per cent of its weight, 
see Engineering and Contracting, Vol. 38 (1912), p. 515. 



24 



ROAD ECONOMICS AND ROAD ADMINISTRATION [cHAP. I 



27. Maximum Load on a Grade. On a grade the effective trac- 
tive power as given by equation (1) is used up in moving the load 
over the road surface and in hfting the load vertically. If L — the 
load, and ix the coefficient of road resistance, then 



and 



{t - g)W = nL + gL, 
t- 



L = 



M + 



w. 



(2) 
(3) 



Equation (3) gives the load that a horse can draw up any grade. 

Table 9 is computed from equation (3) for a value of t equal 
to one tenth of the weight of the horse. The top line of the 
table shows the loads that a horse can draw on the level on the 
various road surfaces; and any column of the table shows the load 
that a horse can pull on any grade for that particular road surface. 

As showing the different effects of grades upon different roads, 
notice that on a muddy earth road a 1 per cent grade reduces the 
load less than one tenth, while on asphalt a 1 per cent grade reduces 
the load more than one half; or, again, notice that with a 5 per 
cent grade, on iron rails the load is less than one twentieth of the 
load on the level, while on the best earth road the load is one fifth 
of that on the level. 

TABLE 9 

Effect of Grade upon the Load a Horse can Draw on Different Roads 
The Load is in terms of the Weight of the Horse 















E. 


VRTH ROA 


D. 


• 


Rate of 
Grade. 


Iron 

Rails. 


Sheet 
Asphalt. 


Broken 
Stone. 


Stone 
Block. 








Ref. 
No. 








Per Cent. 


M= 5ffo- 


M = ino- 


M=B'iy. 


M=5^. 


Best. 


Spongy. 


Muddy. 














f^ = 3*3. 


M = iV- 


1 





20.00 


10.00 


6.00 


5.00 


3.00 


2.00 


1.00 


2 


1 


6.00 


4.50 


3.33 


3.00 


2.09 


1.50 


0.91 


3 


2 


3.20 


2.67 


2.16 


2.00 


1.51 


1.14 


0.67 


4 


3 


2.00 


1.75 


1.49 


1.40 


1.11 


0.87 


0.54 


5 


4 


1.33 


1.20 


1.05 


1.00 


0.82 


0.66 


0.43 


6 


5 


0.91 


0.83 


0.75 


0.71 


0.60 


0.50 


0.33 


7 


6 


0.62 


0.57 


0.52 


0.50 


0.43 


0.36 


0.25 


8 


7 


0.40 


0.38 


0.34 


0.33 


0.29 


0.25 


0.18 


9 


8 


0.24 


0.22 


0.21 


0.20 


0.18 


0.15 


0.11 


10 


9 


0.15 


0.10 


0.09 


0.09 


0.08 


0.07 


0.05 


11 


10 


0.00 


0.00 


0.00 


0.00 


0.00 


0.00 


0.00 



Table 9 shows the load a horse* can draw upon different grades 
and different road surfaces when exerting a uniform pull equal to 



ART. 1] 



ROAD ECONOMICS 



25 



one tenth of its weight. If we desire to know the maximum load 
which a horse can draw up any grade, we must insert in equation 
(3) the maximum value of t and compute the corresponding value 
of L. The value of t to be used in this computation will depend 
upon the length of the grade and upon the frequency with which it 
occurs. If the grade is only a few hundred feet long, it will probably 
be safe to assume a pull equal to one fourth of the weight of the 
horse; but this value should be assumed only for the maximum grade, 
since such pulling is too exhausting for continuous work. 

Table 10 presents the same data as Table 9, but in a slightl}^ 
different form. 

TABLE 10 

Load which a Horse can Draw on a Grade in Terms of the Load on the 
Level when Exerting a Uniform Force Equal to One Tenth of its 
Weight 















Earth Road. 




Rate of 
Grade, 


Iron 
Rails. 


Sheet 
Asphalt. 


Broken 
Stone. 


Stone 
Blocks. 








Ref. 










Per Cent. 


M = 25U. 


M = T^S- 


M = ^0. 


u=^V 


Best. 


Spongy. 


Muddy. 


1 





1.00 


1.00 


1.00 


1.00 


1.00 


1.00 


1.00 


2 


1 


0.30 


0.45 


0.56 


0.60 


0.62 


0.75 


0.91 


3 


2 


0.16 


0.27 


0.36 


0.40 


0.50 


0.57 


0.67 


4 


3 


0.10 


0.18 


0.25 


0.28 


0.37 


0.44 


0.54 


5 


4 


0.07 


0.12 


0.17 


0.20 


0.27 


0.33 


0.43 


6 


5 


0.04 


0.08 


0.12 


0.14 


0.20 


0.25 


0.33 


7 


6 


0.03 


0.06 


0.08 


0.10 


0.14 


0.18 


0.25 


8 


7 


0.02 


0.04 


0.06 


0.06 


0.10 


0.12 


0.18 


9 


8 


0.01 


0.02 


0.04 


0.04 


0.06 


0.08 


O.ll 


10 


9 


0.01 


0.01 


0.02 


0.02 


0.03 


0.04 


0.05 


11 


10 


0.00 


0.00 


0.00 


0.00 


0.00 


0.00 


0.00 



28. The maximum load which a horse can draw upon any road, 
particularly upon the steepest grade, is not, however, necessarily 
proportional to the rate of grade and to the resistance, since the 
pull that a horse can exert depends upon the foothold. Owing 
to the danger of slipping on steep grades, particularly when the 
road is wet or icy, it is not customary to lay sheet asphalt on grades 
of more than 4 per cent, or ordinary stone blocks on grades of more 
than 10 per cent. On steeper grades, special forms of stone blocks 
are sometimes employed to increase the tractive power by affording 
better foothold for the horses. 

29. Travel Census. A knowledge of the use made of a road or 
pavement has an important bearing on questions of construction, 



26 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

maintenance, and cleaning. The travel determines the amount of 
money that may economically be spent in reconstruction, and also 
fixes the width and character of the improved portion. The use 
made of the road or street is necessary to determine the amount of 
service obtained from any particular road surface. Further, the 
cost of cleaning a pavement depends upon the character of the sur- 
face and the travel; and unless the latter is known, it is impossible 
to make any instructive comparison between the cost of cleaning 
different surfaces. 

30. History. It is surprising that but few travel censuses have 
ever been taken. Except in France, not much attention has been 
given to this subject in Europe. The French engineers have made a 
very careful study of the amount and effect of travel on the rural 
roads. Previous to 1844 travel data had been collected in certain 
locahties; but from 1844 to 1903 ten censuses of national scope 
were taken, and it is planned to take one every 10 years. 

The results of the French observations are not of much value in 
America because of the difference in conditions; and results before 
about 1906 are not of much value because of the recent introduction 
of the automobile. 

31. American Roads. The Massachusetts Highway Commission 
in 1909 had a travel census taken upon state-aid highways for 14 
hours per day for seven days at 238 stations, and in 1912 a similar 
count was made at 156 stations, and in 1915 at 192 stations. At 
the same time a travel census was taken at a number of points on 
the roadways of the Metropohtan and the Boston Park Systems. 
The methods and results are presented in the respective annual 
reports. 

The observer separated motor-driven vehicles into three classes, 
and horse-drawn into four. These classes and the assumed weight 
of each (taken according to the prevailing practice in Great Britain) 
are as follows : 

Motor-Driven Vehicles: Weight 

Runabouts 1 . 35 tons 

Touring cars 2.23 " 

Trucks 6.25 '' 

Horse-Drawn Vehicles: 

l-horse, light 0.36 '' 

1- " heavy 1.12 '' 

2 or more horses, hght . 54 " 

2 " " heavy 2.46 " 



ART. 1] 



ROAD ECONOMICS 



27 



In the first three years motor travel on the rural roads increased 
130 per cent, and in the second three years 150 per cent; while the 
horse-drawn vehicles decreased almost exactly 20 per cent in each 
period. In 1912 the motor-driven vehicles were 63 per cent of the 
horse-drawn, but in 1915 they were 497 per cent. The total travel 
increased about in proportion to the number of motor cars registered. 
As the number of motor cars in this country is rapidly increasing 
(for example, the number made in 1916 was 80 per cent greater than 
in 1915), it is Ukely that travel on public highways will continue to 
increase. 

A summary of this census for a few roads is shown in Table 11; 
and incidentally this table also shows the use of travel census 
data in determining the unit cost of maintenance. The wide 
variation in the cost of maintenance of these roads is probably 
due to differences in the age or character of the surface and to dif- 
ferences in the character of the traffic. 

i 

TABLE 11 ' 

1 
Travel and Cost of Repairs on Massachusetts State-Aid Roads 



Road. 



Ashley 

Beverly (No. 1) . . . . 

Hamilton 

Lynn 

Medford-Somerville 

Milton 

Sangus 

Shrewsbury 

Truro 

Weston 



Motor-Drawn 
Vehicles. 



14 
60 
86 

194 
44 
15 
15 
76 
7 

115 



65 

278 

334 

1 365 

121 

50 

58 
407 

63 
533 



Horse-Drawn 

Vehicles. 



Single 
Horse. 



70 
66 
75 
28 
47 
30 
25 
64 
15 
167 



16 
46 
39 
19 

198 
77 

190 
60 
14 
98 



Two or 
More. 



14 
12 
27 
14 
193 
88 
65 
36 
3 
59 



Total 
Traffic. 



271 
1618 
1 199 
3 468 
1332 
1 140 
1022 
1305 

186 
1918 



4) CO 

Co 
c£2. 



81 150 
485 220 
359 730 
1 040 430 
399 570 
342 210 
306 660 
391 550 

55 770 
575 280 



Cost of 
Mainte- 
nance. 






$ 266 
1 104 

200 
1 081 
1031 

592 
1 334 

510 

143 
1 040 



o 

^ 'k 

Qi ft 



O 

0.38 
0.23 
0.06 
0.10 
0.26 
0.17 
0.44 
0.13 
0.25 
0.18 



The use of a travel census in determining the character of a road 
surface fitted to particular traffic conditions is incidentally illustrated 
in Table 26, page 177. 

32. In 1906 the Illinois Highway Commission took a census of 
travel at 71 stations at various times during one year.* Observa- 



* Annual Reports for 1906 and 1907. 



28 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

tions were made of only the number of vehicles without distinction 
as to their character or weight. Twelve of the roads had about 75 
vehicles per day, twenty-seven about 145, and ten about 250. The 
results seem to show that there is no relation between the travel on a 
road and the population of the near-by town; or, in other words, 
that there are roads in the vicinity of even very small towns that 
have as much travel as roads near large cities. 

33. In the summer of 1917 the Iowa Highway Commission took a 
census of travel on a few of the main roads. Observations were made 
at each station for ten days; and all vehicles were actually w^eighed. 
A record is to be made of farm traffic, of town and city traffic, and of 
tourist travel, with the hope of securing data for an equitable appor- 
tionment of road expenditures. A prehminary report on observa- 
tions made during the tourist season at eight stations on an earth- 
surface tourist highway leading into important market centers, 
showed 3 per cent tourist travel, 87 per cent interurban traffic, and 
10 per cent farm traffic. 

34. American Streets. The first travel census in the United 
States was carried out by the Barber Asphalt Co. in New York City 
and less elaborately in ten other cities in 1885.* The record 
shows the total number of vehicles and the number of tons per 
foot of width of pavement. The same company took a similar 
census in New York City in 1904.t In both cases the count was 
limited mainly to asphalt and granite-block pavements. Since 1913 
the city of St. Louis, Mo., has taken an annual travel census — at 
first on business streets, but later also on residence streets, t In 
New York and St. Louis there was a very great annual increase in 
the amount of travel. In St. Louis from 1914 to 1915 the increase 
was 20 per cent, the increase in motor-driven traffic being 53 per cent 
and the decrease in horse-drawn 15 per cent. A few other records 
of various kinds have been made in several cities. 

35. Classification of Traffic. The data collected in a travel census 
should be such that, in addition to being used for local comparisons, 
they should be such as to permit comparisons with data taken in 
other localities. There is no standard method of classifying the 
vehicles, or of the assumed weight of the different vehicles, or of 
fixing the width of the traveled way. Further, the density of travel 
is sometimes stated by giving simply the number of vehicles per day 

* Trans. Amer. Soc. of C.E., Vol. 15 (1886), p. 123. 

t Ibid., Vol. 57 (1906), p. 181-90. 

t Engineering News, Vol. 76 (1916), p. §32-34. 



ART. 1] ROAD ECONOMICS 29 

or per year; but usually by giving the number of tons per year per 
foot of width. The unit for comparing the cost of maintenance 
is either the tons per year per foot of width or the ton-miles per 
year. 

The classification and weights of the vehicles in the Massachusetts 
census are shown in § 31. Apparently the width of the traveled 
way was taken as the full width of the improved portion, — as it prob- 
ably is in a narrow rural road. For a somewhat similar classifica- 
tion and schedule of weights employed by several road and pave- 
ment constructing companies, see page 149 of the 1912 Proceedings 
of the American Society of Municipal Improvements. 

36. Weight of Vehicles. The following classification and sched- 
ule of weights has been recommended.* The weight of the horse is 
to be considered as a part of that of the vehicle ; and the ton is 2,000 
pounds. 

Horse-Drawn Vehicles Motor-Driven Vehicles 

Number of Horses. ^tfns^' ^^^^^ ^-^ Automohile. ^tons^' 

Single horse without vehicle .... . 50 Motorcycle or bicycle . 15 

1-horse vehicle, light 1 .20 2-passenger automobile 1 .30 

1-horse vehicle, heavy 2 . 00 Over 2-passenger automobile. . . 2 . 20 

2-horse vehicle, light 2 . 00 Freight motor-truck, light 6 . 30 

2-horse vehicle, heavy 4 . 00 " " medium . . 6 . 00 

3-horse vehicle 5.00 " " heavy 8.50 

4-horse vehicle 6 . 00 

37. Width of Traveled Way. The effective traveled width of a 
street is sometimes taken as 3 feet less than the width between curbs. 
In many cases, particularly adjacent to car tracks and where auto- 
mobiles are parked along the curb, most of the travel is concentrated 
upon a comparatively narrow portion of the pavement, f The 
results should be stated in tons per foot of total width, and also in 
tons per foot of maximum traveled width. 

If the several classes of traffic are segregated into different fines 
of travel, the details should be stated. 

38. Diversion of Travel. In any investigation of traffic conditions 
preliminary to any improvement in either the location or the surface 
of a road, careful attention should be given to the probable effect 
of the improvement in diverting travel to the road or street. Some- 



* W. H. Connell, Chief of Bureau of Highways, Philadelphia, Engineering and Contracting, 
Vol. 47 (1917), p. 227. 

t For diagrams showing this concentration, see Engineering News, Vol. 78 (1917), p. 201-2. 



30 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

times a small change in the condition of the road makes a radical 
change in the amount and character of the travel. 

39. WEIGHT AND WIDTH OF VEHICLES. Formerly the only 
excessive loads hauled over rural roads or city streets were heavy 
pieces of building or bridge material, machinery, etc., hauled on 
horse-drawn vehicles, and steam traction-engines; but as these 
vehicles were not very numerous and as the speed was low, no serious 
harm was done, particularly where traction engines were required to 
remove or cover the mud lugs. In the last ten years the advent of 
heavy high-speed motor trucks has greatly increased the loads and 
speeds of vehicles using the highways. Certain types of motor 
vehicles now in use are too heavy for the present roads or pavements, 
and much damage is being done; and furthermore the number and 
weight of such vehicles is rapidly increasing. It is inequitable and 
impracticable to reconstruct all or even many of the roads and pave- 
ments so as to enable them to carry safely such motor-driven vehicles. 
Therefore special taxes are being levied upon heavy motor-driven 
vehicles, partly to make them partially pay for the damage done to 
the highways, but chiefly to prevent further increase in their number 
and weight. Some of the states have laws regulating the load per 
width of tire and also the speed, and some regulate also the diameter 
of the wheel.* The following is from an ordinance recently passed 
in New York City.t 

License Schedule for Motor Trucks in New York City 

" (a) Vehicles carrying or intending to carry a total gross load of 6,000 lb. 
or less upon any wheel shall be charged the following annual license fee : 

Load in Pounds License Fee 

■per Inch Width for 

of Tire. Each Vehicle. 

700 or less $1 

751 to 800 3 

801 to 850 6 

851to900 12 

901 to 950 25 

951 to 1000 50 

" (6) In addition to the fees provided in subdivision (a), further fees shall be 
charged for loads greater than 6,000 lb. upon any wheel, but not exceeding 10,000 
lb., as follows: 



* For the laws regulating motor trucks in a number of states an<J cities, see Engineering News, 
Vol. 76 (1916), p. 938-39. 

t Engineering Record, Vol. 73 (1917), p. 790. 



ART. 2] ROAD ADMINISTRATION 31 

Weight in License' Fee 

Pounds per for 

Wheel. Each Vehicle. 

6 000 to 6 500 $75 

6 501 to 7 000 110 

7 001 to 7 500 150 

7 501 to 8 000 200 

8001 to 8500 300 

8 501 to 9 000 500 

9 001 to 9 500 750 

9 501 to 10 000 1 000 

" For loads greater than 10,000 lb. per wheel, Hcense fees shall be charged 
for each vehicle at the additional rate of $500 for each 1,000 lb. per wheel increase 
in weight, provided no load greater than 1,000 lb. per inch width of wheel shall 
in any case be permitted, except as specified in subdivision (d) . 

" In Ueu of the fees hereinabove provided for in subdivisions (a) and (6) for 
loads of 6,000 lb. or more on any wheel, special permits may be issued for single 
trips and fees charged therefor at the rate of 10 per cent of the fees therein pro- 
vided, except that no single fee shall be less than $25. 

" (c) Vehicles 6 feet 6 inches or more in width over all shaU be charged, in 
addition to the fees specified in subdivision (a) and (6), the following annual 
fee; 

Width of Vehicle License Fee 

for each inch in 

width in excess 

of 6 feet 6 inches. 

6 feet 6 inches to 7 feet inches $5 

7 " " 7 '' 6 '' 10 

7 " 6 " 8 '' 8 '' 15 

8 " " 8 '' 6 '' 20 

8 " 6 " 9 " 6 " 25 

" (d) In Ueu of the fees provided in subdivision (c) for excess width of vehicle, 
special permits for single trips may be granted upon payment of single fee of not 
less than $10." 

Art. 2. Road Administration 

41. Administrative Unit. In this country until recently, the 
management of roads rested upon local authorities, either those of 
townships or counties. In those cases in which the administration of 
road affairs was nominally in the hands of the county authorities, 
nothing was usually done except to divide the county into road dis- 
tricts and virtually transfer all authority to local officials appointed 
for that purpose. Apparently it is impossible to secure either good 
roads or an efficient road administration by the action of officials 
who have only local authority, and who are necessarily swayed by 
purely local, if not individual, interests. This is not pecuHar to 



32 ROAD ECONOMICS AND ROA.D ADMINISTRATION [cHAP. I 

America, since great difficulties have always been encountered in 
maintaining a system of public highways by any locally governed 
community. 

The fundamental difficulty is that the small administrative unit 
makes it impossible to secure efficient supervision, since the time 
necessarily required in road administration is but an incident among 
private or official duties. Another difficulty is that the official is 
usually elected for political reasons, rather than for his abihty in 
matters relating to the roads. A further difficulty is that the tenure 
of office is short, and successive officials have confficting views as to 
road administration and road improvement. 

Another objection to the small administrative unit is the improb- 
abihty of the district's having suitable machinery in sufficient 
quantity to effectively and economically care for the roads. 

42. State Aid. — In 1891 the state of New Jersey inaugurated a new 
departure in road administration in the United States — that of state 
aid in road construction. In 1917 all of the states except Mississippi 
and South Carolina had adopted some form of state aid. The fun- 
damental principle of state aid is that some roads are built at the 
joint expense of the state and local authorities. The states differ 
greatly as to (1) the proportion paid by the state, (2) the amounts 
paid by the county, township, and abutting property, (3) the amount 
md the method of the supervision over the construction, and (4) 
the authority that maintains state-aid roads. 

The adoption of state aid led to the establishment of state high- 
way departments in many of the states; but to participate in federal 
aid (see § 45) it was necessary for a state to have a state highway 
department, and hence all of the states now have such departments. 

One of the most important factors in bringing about the rapid 
adoption of state aid and state supervision, has been the introduction 
of the automobile and the consequent development of greater interest 
in good roads. 

43. Table 12 gives data concerning road improvement in the 
several states. 

44. The principle of state aid is defended on the ground that 
(1) it secures centraUzed, and therefore more efficient, control; (2) 
makes the wealth of the city bear part of the expense of maintaining 
the country roads; and (3) compels the railroads and other state- 
wide corporations to bear part of the expense of local improvements. 
The chief advantage of state aid is that it secures uniform and more 
intelligent supervision than is possible — on state-aid roads at least — 



ART. 2] 



ROAD ADMINISTRATION 



33 



TABLE 12 
Road Mileage and Road Expenses in the Several States 



State. 


Miles of 


Rural Public Roads. 


Year 
Original 

State- 
Aid Law 
Passed. 


State 
Aid in 
in 1915. 


Total 
Cash 
Expendi- 
tures in 
1915. 


Total 
Surfaced 
Roads in 

State. 


Total 
Public 
Rural 
Roads in 
State. 


Percent- 
age of 
Surfaced 
Roads in 
1915. 


Alabama 

Arizona 

Arkansas . 


5 915 

350 

1 200 

13 000 
1750 
3 200 

300 

3 500 

13 000 

950 
11000 
27 000 

1 000 
1250 

13 000 

2 250 

3 000 
2 950 

8 800 
8 600 

5 500 

2 500 

8 000 
775 

500 

75 

1800 

4 600 
450 

17 500 

6 500 
1 100 

30 920 

300 

7 780 

9 883 

1 246 

3 500 
850 

8 625 
12 000 

1053 

3 478 

4 760 

5 460 

1 200 

14 050 
500 


55 446 
12 075 
50 743 

61038 
39 691 

14 061 

3 674 

17 995 
84 770 

23 109 
94 141 
63 370 

106 847 
111 536 

57 916 

24 562 

25 528 
16 458 

18 681 

74 089 
93 500 

45 778 
96 124 
39 204 

80 338 

15 000 
14 020 

14 817 
11873 
80 112 

50 758 
68 000 
86 453 

107 916 
36 819 
91 556 

2 121 
42 220 
96 306 

46 050 
128 960 

15 000 

15 082 
53 388 
42 428 

32 024 

75 702 
14 381 


10.7 
2.9 
2.3 

21.3 

4.4 
22.7 

8.0 
19.4 
15.3 

4.1 
11.7 
42.6 

1.0 

1.1 

22.1 

9.1 
11.7 
17.9 

46.6 

11.6 

5.9 

5.5 
8.3 
2.0 

.6 

.5 

12.8 

31.0 

3.8 

21.8 

12.8 

1.6 

35.8 

.3 
21.1 
10.8 

58.8 

8.3 

.9 

18.7 
9.3 
7.0 

23.1 

8.9 

12.8 

3.7 

18.5 

3.5 


1911 
1909 
1913 

1895 
1909 
1895 

1903 
1915 
1908 

1905 
1905 
1917 

1904 
1911 
1912 

1910 
1901 

1898 

1892 
1905 
1905 

■■1967" 
1913 

1911 
1911 
1903 

1891 
1909 

1898 

1901 
1909 
1904 

1911 
1913 
1903 

1902 

"igii ' 

1915 
1917 
1909 

1898 
1906 
1905 

1909 
1911 
1911 


$126 134 

476 178 

25 000 

8 301 149 

203 000 

2 084 944 

31000 
1 135 


$4 283 207 

1 076 178 

2 803 000 


California 


20 753 281 
2 193 000 


Connecticut 

Delaware 

Florida. . . 


3 484 944 

397 500 
5 501 135 


Georgia 


3 700 000 


Idaho 


200 000 
818 638 


1 974 636 


IlUnois 


9 263 995 


Indiana . 


13 000 000 


Iowa. . 


80 935 

10 000 

573 715 

144 821 

1 009 345 
3 330 000 

2 634 567 
975 000 

1 580 000 


13 606 299 




5 510 000 


Kentucky 

Louisiana.. . . 


3 122 430 
3 569 709 


Maine 


3 293 902 


Maryland 

Massachusetts. . . . 


5 630 000 

6 557 279 
10 174 738 


Minnesota 

Mississippi. ...... 

Missouri . . 


8 292 000 
2 900 000 


369 189 
18 346 

120 000 


8 369 189 




3 676 318 


Nebraska 


3 520 000 


Nevada* 


250 000 


New Hampshire. . . 

New Jersey 

New Mexico 

New York 

North Carolina 

North Dakota .... 
Ohio 

Oklahoma . . . • 

Oregon 

Pennsylvania 

Rhode Island 

South Carolina. . . . 
South Dakota 

Tennessee 

Texas 

Utah 


666 339 

1 163 308 

152 122 

13 983 769 

10 000 


2 363 414 

7 163 584 

584 919 

24 255 648 

5 510 000 
2 500 700 


3 442 604 

10 000 

230 000 

6 541 257 

204 119 


12 975 688 

3 410 000 

6 182 000 

12 541 257 

594 119 
1 000 000 




1 450 000 


3 500 


3 503 500 
9 500 000 


121 000 

485 145 

526 645 

1 435 020 

9 212 

1 389 515 

5 000 


1 213 100 




1 475 145 


Virginia 


4 018 3QQ 


Washington 

West Virginia 

Wisconsin 

Wyoming 

Total 


6 670 702 

2 759 212 

9 960 980 

441 291 


276 920 


2 451 660 


11.3 




53 491 651 


266 976 399 



34 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

with a smaller administrative unit; and besides the standards set on 
state-aid roads tend to become the ideals for the other roads. 

45. National Aid. In 1916 Congress passed a law granting to 
the several states federal aid in the construction of roads, which 
was another new departure in road administration in this country. 
The law appropriated $5,000,000 for federal aid in 1917, and pro- 
vided to increase the amount $5,000,000 each year until in 1921, when 
the appropriation will be $25,000,000. The U. S. Department of 
Agriculture may deduct 3 per cent for administrative expenses, and 
the remainder is divided among the several states as follows: One 
third in proportion to the areas of the states, one third in proportion 
to the mileage of star and rural mail routes in the states, and one 
third in proportion to the population according to the preceding 
federal census. The federal money can be used to pay not to exceed 
one half of the total cost of the construction of any road or system 
of roads, the plans for which have been previously approved by 
the proper federal authority. Table 13, pages 36-37, shows the 
official figures employed in making the distribution, and the amounts 
for each state in 1917. 

In Europe nearly all countries give national aid in some form for 
building roads. 

46. Classification of Roads. It has long been known by 

close students that the problems of road administration would be 
greatly improved if the roads were classified according to their im- 
portance, into state, county and township roads, or into county, 
township and neighborhood roads, the roads of each class to be under 
a corresponding administrative authority. One of the incidental, 
but not unimportant, results of the adoption of the state aid has been 
the classification of the wagon roads. It has been found that 10 
to 15 per cent of the roads carry from 80 to 90 per cent of the travel. 
These principal roads are called state or county roads, and are the 
ones upon which the state aid is expended, either directly or indirectly 
under the supervision of state authorities. 

The modification of the state road laws incident to the introduc- 
tion of the principle of state aid has usually resulted in giving to some 
county authority supervision over township road officials. 

47. Road Taxes. How shall the expense of constructing and 
maintaining roads be distributed? This question has been answered 
in various ways in different parts of this country and in different 
countries of Europe. There are three forms of road taxes which 
have long been in use; viz.: (1) a tax upon the traveler, (2) a cap- 




ART. 2] ROAD ADMINISTRATION 35 

itation tax, and (3) a property tax. The first leads to toll roads; 
and the second is usually called a poll tax. 

In 1901 the State of New York introduced a method of raising 
revenue for road purposes, viz. : a license for operating automobiles. 
For present purposes this will be referred to as the automobile road 
tax. 

48. Toll Roads. These are conducted on the theory that the 
travelers over a road are the recipients of its benefits and should 
pay for its support. Toll roads are justifiable only in a new country 
where the amount of taxable property is small, and where for long 
stretches of territory there are few inhabitants, since such roads 
induce the investment of capital that possibly the pioneer or the new 
community could not afford; and even under these conditions they 
are practicable only where there is considerable traffic. In early 
times the government collected the toll and used it for the main- 
taining and extension of the road; but later toll roads were usually 
in the hands of private capitalists. 

Toll roads are objectionable owing to the proportionally great 
expense of collecting the revenue, and owing to the fact that they 
are managed solely with reference to securing returns upon the 
capital invested and without regard to the interests of the public. 
The only remedy for the evils of the system is for the public to sup- 
port the roads. Roads are an indispensable public convenience 
— a benefit to every citizen, whether a direct user of the road or not, — 
and consequently should be maintained by a universal tax. At 
present the toll system is regarded as unwise for both economic and 
political reasons; and toll roads have almost entirely been abolished 
both in this country and in Europe. 

49. Poll Tax. Notwithstanding the fact that most writers on 
political economy consider a capitation tax an undesirable form 
of taxation, nearly all of the states levy a poll tax for road purposes. 
Apparently it is the only capitation tax in this country. It is not 
wise to occupy space here to inquire into either the wisdom or reason 
for this form of road tax. 

Almost universally the law permits the payment of the poll 
road-tax in money or labor, and it is usually paid in labor. In the 
poorer and less populous states, this tax is nearly the sole support 
of the road system. In many states there are numerous exemptions, 
and in all states the tax is difficult to collect, and consequently 
the poll tax is an unimportant element in road construction and 
maintenance. 



36 



ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. 1 



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ART. 2] 



ROAD ADMINISTRATION 



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38 ROAD ECONOMICS AND ROAD ADMINISTRATION [cHAP. I 

50. Property Tax. There are three forms of the property road 
tax : the special assessment, the direct tax, and the general tax. 

In many states when any considerable road improvement is 
contemplated, part or all of the cost of the same is laid as a special 
tax or assessment on all real estate within some certain distance of 
the improvement. In Indiana at one time, this distance was two 
miles; and in Wisconsin, three. Ordinarily this tax is not uniform 
over the included area, but is graded according to the supposed 
benefits. This tax is usually payable in money. 

In most of the states, the territory is divided into small units, 
called road districts, and a uniform road tax is laid upon all prop- 
erty within the district. Usually this tax may be paid in either 
money or labor; and when so permitted, is usually paid in labor. 

In most states there is also a general property tax for road and 
bridge purposes, which must be paid in money. 

In poorer communities the roads are cared for principally by 
the district road tax, which is usually paid in labor; but in wealthier 
communities the general property road and bridge tax (cash tax) 
is greater than the district road tax (labor tax) . 

51. Labor vs. Money Tax. In most of the states the labor tax 
is still regularly employed, although it is gradually disappearing. 
The labor-tax system was inherited from England, and is a survival 
of the feudal method of requiring all able-bodied men to render public 
service. England and France have a labor road-tax, but upon a 
much less extensive scale than has this country. 

The roads and streets of the cities, towns, and villages are usually 
under the control of the municipalities, in which as a rule the labor 
tax does not exist ; and therefore the labor-tax system appHes chiefly, 
if not wholly, to rural communities. Further, since a very large pro- 
portion of the roads are of earth, the labor-tax system is usually 
applied to the construction and care of only earth roads. 

It is common to assume that the labor-tax system is aU wrong, 
and that its evils would be escaped by paying road taxes in money. 
The labor tax has inherent disadvantages, but many of the defects 
charged to it belong rather to defective administration and to the 
system that leaves the control of the pubHc highways to a small 
locally-governed community. 

The objections to the labor-tax system are: 1. The labor is 
indifferent and inefficient. 2. It is impossible to get the work done 
at the most suitable time. 3. The system allows no selection of the 
laborer. All of these are important considerations. 



ART. 2] ROAD ADMINISTRATION 39 

The reply to the above objections is usually about as follows: 
1. The farmer is wilhng to pay more in labor than in money, which 
compensates in part, at least, for the objections to the labor-tax 
system. This preference is not peculiar to the American farmer. 
In France, if the road tax is paid in money, a reduction of 40 to 50 
per cent is made; but still 60 per cent of the people prefer to pay in 
labor. Farmers not infrequently give more both in labor and 
money than is exacted as road taxes, because they are interested 
in better roads. 2. In many rural communities it is impossible to 
secure any one to do road work at reasonable wages at the most 
suitable season. 3. If the tax were paid in money, there is no 
certainty that the labor would be any more efficient. Streets are 
maintained under the cash-tax system, but the labor is not ideally 
efficient. The authority that virtually wastes the labor tax will 
probably also waste the cash tax. 

52. The labor tax is not necessarily the cause of inferior roads, 
nor the cash-tax system in itself the cause of improved roads. Town- 
ships under the labor-tax system often have better roads than 
adjoining townships under the cash-tax system. The one thing 
absolutely necessary for successful road management is effective 
supervision of the work. Without it neither system will accom- 
pUsh much, and with it either system will do reasonably weU. 

Many townships have changed from the labor-tax system to the 
cash-tax system with a marked improvement in the condition of the 
roads — due chiefly, if not wholly, to better administration. In these 
cases the public sentiment that demanded road improvement secured 
the change from the labor tax to the cash tax; and, consciously or 
unconsciously, also secured a more efficient road administration. In 
many of these cases the so-called cash-tax system is practically 
only a change in the method of administering the labor-tax system, 
since farmers desiring to do so are given an opportunity to work out 
their road taxes under the cash system. Under the labor-tax system 
those working upon the roads receive credit on their road taxes, 
while in the so-called cash system the laborer usually receives an 
order which is accepted as cash in pa3dng taxes. 

The labor-tax system is more objectionable with roads having a 
hard surface than with earth ones, since the construction of the 
former is more difficult and their maintenance requires intimate 
knowledge and constant attendance, and also since the former are 
built only where there is much travel and where the labor of main- 
tenance is greater. Thi^ subject will be considered incidentally 



40 ROAD ECONOMICS AND ROAD ADMINISTRATION [CHAP. I 

under Maintenance in the chapters on earth, gravel, and broken- 
stone roads. 

53. Automobile Tax. Since 1901 the several states have adopted 
the system of Ucensing automobiles as a means of securing revenue 
for road purposes. In 1916 the gross revenue from this source 
amounted to $25,865,370, of which 92 per cent was applicable for road 
work; and the net amount so applied was nearly 9 per cent of the 
total expenditures for rural roads and bridges in the United States. 
About 70 per cent of the total automobile revenue is expended under 
the supervision of the State Highway Departments. 

In 1916 there was an average of 1.4 motor cars for each mile of 
rural public roads in the United States, and the number of motor cars 
is increasing, the increase in 1915 being 40 per cent and in 1916 43 
per cent. The average annual registration or license fee per motor 
varies between the several states from 50 cents to $19.67. The 
tendency in all of the states is to increase the fee. 

54. Comparison of Road Expenditures. From 1904 to 1915 the 
annual expenditures on the rural roads and bridges in the United 
States increased from about $80,000,000 to about $282,000,000, an 
increase of more than 2 J times. During the same period the annual 
expenditures for state-aid road and bridge construction and main- 
tenance increased from $2,550,000 to $53,492,000, an increase of 
20 times. In 1904 the local bond issues for roads and bridges 
amounted to $3,530,000, but in 1915 amounted to about $40,000,000. 
In 1904 the expenditure for roads under state supervision was 6 per 
cent of the total road expenses; but in 1915 it was 30 per cent, or 
more than the total expenditure for roads in 1904. 

In 1904 about one fourth of the total expenditures for roads and 
bridges was paid in labor. From 1904 to 1915, while the total 
expenditures for roads and bridges have increased 3 J times, the por- 
tion from local bond issues about 1 1 times, and that from state aid 
20 times, the portion from the labor road-tax decreased about half. 

In 1904 the actual cash road and bridge expenditure in the 
United States averaged slightly less than $28 per mile of rural roads; 
but in 1915 it had increased to an average of $109 per mile of road. 

55. The magnitude of the above sums shows the importance of 
the present road expenditures, and also the probability that such 
expenditures will increase greatly in the future. Road construction 
and maintenance is already a matter of great importance to the pubHc 
and to the engineering profession, and is likely to increase rapidly. 



CHAPTER II 
ROAD LOCATION 

58. Elements Involved. In general the determination of the 
best location for a road requires a study of the topographical fea- 
tures of the region through which the road is to pass, and also an 
investigation of the nature and amount of the traffic to be provided 
for. Viewed as a question of economics, the best location is that 
for which the sum of the interest on the cost of construction and of 
the annual cost of maintaining the road and of conducting trans- 
portation over it, is a minimum. The location of a wagon road is 
not, however, entirely a question of economics, since the location 
should be made with reference to the convenience and comfort, 
and perhaps also to the pleasure, of those who use it ; and is frequently 
more of a social question than one of economics. Only the economic 
features of location will be considered here, and they but briefly. 

However, in locating a new road, it is well to remember that the 
location will probably serve for many generations, and perhaps for all 
time, as the growing importance of the surrounding country and the 
location of buildings and of division lines of the land with reference 
to the road make it increasingly more difficult and expensive to change 
the location. Thus the location of a road is a field where costly 
errors and permanent blunders may creep in and forever fasten 
themselves upon the road and its users; and, worst of all, these errors 
become more costly as the use of the road increases. 

Over most of the United States, the roads are in the main already 
located, and the necessity for the location of new ones does not often 
arise; and hence as a rule, the only application of the principles of 
economic location will be in the re-location of comparatively short 
stretches of road. The original location may have been fit and proper 
when the region was new and undeveloped, but the increase in the 
amount and the change in the character of the traffic may justify a 
very considerable change. There are many rural roads that could 
be materially improved by a careful re-location. 

41 



42 ROAD LOCATION [CHAP. II 

59. Rural roads are used by both horse-drawn and motor-driven 
vehicles; and strictly each class of vehicles should be considered in 
solving problems of road location. However, the passenger auto- 
mobile need not be considered, since with the variable speed and high 
power of its engine, it can overcome any grade that can be econom- 
ically used by horse-drawn vehicles, and since the cost of transpor- 
tation by a motor-driven vehicle is small it may be neglected in 
computing the effect of shght differences in distance; and therefore 
the passenger automobile may be disregarded in problems of road 
location. Automobile trucks need not be considered for the same 
reasons as above, and also as they are much less common on typical 
rural roads than horse-drawn vehicles. 

60. The principles to be observed and the methods to be em- 
ployed in making the location of a wagon road are substantially the 
same as those used in the location of a railroad. The method of 
examining the country and of making surveys will not be considered 
here, as such subjects are elaborately presented in treatises on rail- 
road location. 

The fundamental principles appHcable in locating a new rural road 
or in improving an old one will be briefly considered; but no hard 
and fast rules can be laid down, for each road must be designed for 
the place it is to occupy and the service it is to render. In the loca- 
tion of any road there will always be an opportunity to exercise 
keen insight and good judgment. 

The subject will be considered under the five heads: distance, 
grades, curves, width, and placing the Hne. 

61. Distance. Other things being equal, the shorter the road 
the better, since any unnecessary length causes a constant threefold 
waste: (1) the interest on the cost of constructing the extra length; 
(2) the ever-recurring cost of repairing it, and (3) the time and labor 
employed in travehng over it. However, the advantage of straight- 
ness, i. e., of shortness, is usually greatly over-estimated. The dif- 
ference in length between an absolutely straight hne and one deflect- 
ing a little to one side is not very great. For example, in Fig. 3, if 

A B = BC = 1,000 feet, smd B D = 10 
feet, the line A B C is only one tenth of a 
foot longer than the line ADC. If 
A B = BC = 1 mile, and B D = 300 
feet, the line A B C is only 17 feet longer 
than ADC. ''' If a road between two places ten miles apart were 
made to curve so that the eye could nowhere see more than a quarter 




DISTANCE 43 



of a mile of it at once, its length would exceed that of a perfectly 
straight road between the same points by only about one hundred 
and fifty yards." 

One of the most common defects of ordinary country roads is 
that distance has been saved by a disregard of the desirabihty of 
easy gradients. The curving road around a hill may often be no 
longer than the straight one over it. The latter is straight only 
with reference to the horizontal plane, but curved as to the vertical 
plane; while the former is curved as to the horizontal plane, but 
straight as to the vertical plane. Both Knes curve, and the one 
passing over the hill is called straight only because its vertical curva- 
ture is less apparent to the eye. 

62. Value of Saving Distance. Theoretically the value of a dif- 
ference in length may be computed by determining (1) the amount of 
traffic, (2) the cost per ton-mile, and (3) the total coat of conducting 
the traffic; and then assuming that the value of any difference of 
length is to the total cost of transportation as the difference of the 
length is to the total length. If the annual cost of conducting trans- 
portation over a given road is known, then this cost divided by the 
length of the road gives the annual interest upon the sum that may 
be reasonably expended in shortening the road 1 mile, i. e., the value 
of a saving of a mile of distance ; and of course dividing this sum by 
the number of feet in a mile will give the value of saving 1 foot of 
distance. 

Unfortunately it is not possible to determine the amount of 
traffic with any considerable degree of accuracy. At some railroad 
stations the sole freight shipped out is agricultural produce, in which 
case the traffic over any particular wagon road can be approximated 
by distributing the shipments according to the contributing area. 
The average load can be determined with sufficient accuracy by con- 
sulting the records of the grain dealers. In addition to the above, 
which may be called the heavy freight traffic, there is a considerable 
amount of light freight and passenger traffic which would be bene- 
fited by a saving of distance. 

For the sake of working out an example, it will be assumed that 
the cost of transportation is 10 cents per ton-mile. This cost is 
made up of the cost of loading and unloading, of driving, of feed, 
and of wear and tear of horses, wagon, and harness. The cost of 
loading and unloading is independent of distance. The cost of 
driving nominally varies as the time, i. e., as the distance (see third 
paragraph of § G3). The cost of wear and tear varies as the distance; 



44 ROAD LOCATION [CHAP. II 

but the cost of feed does not so vary. It is impossible to assign 
reliable values to these several factors of the cost, but it is certain 
that only part of the cost of transportation varies as the distance; 
and for the sake of completing the illustration, it will be assumed that 
8 cents per ton-mile varies as the distance. This sum multiplied by 
the number of tons passing over the road in a year will give the sum 
that may be spent annually to secure a saving of 1 mile of distance. 
For example, a road leading to a certain village was originally 
laid out on the east and north sides of a quarter-section, but on 
account of low ground on the northeast corner another road was 
opened on the south and west sides. The quarter-section was one 
large field. How much expense would the traffic justify in order to 
secure a road diagonally through the quarter-section. The heavy- 
freight traffic was approximately 3,000 loads of 1 ton each per annum. 
The annual value of saving 1 mile would then be 8 cents X 3,000 = 
$240. The saving in distance by going through the quarter-section 
is 0.29 mile; and the annual value of saving this distance is $240 X 0.29 
= $69.60. The diagonal road would occupy 2 J acres less land 
than the longer one; and as the land rented for $3 per acre, this 
adds $3 X 2J = $7 per annum to the value of the diagonal road. The 
annual saving from these two items is then $69.60 + $7.00 = $76.60. 
This is the interest at 5 per cent on $1,532, which sum, according to 
the above computations, could be borrowed, and used to secure this 
improvement, and the community be no worse off financially. 

In addition, there would be some advantage to the fight freight 
and passenger traffic by shortening the road, but it was difficult, if not 
impossible, to estimate this saving; and as the benefit per trip 
would probably be less than for the heavy freight traffic, it was 
neglected. There would be a sfight saving in the cost of mainte- 
nance of the shorter road, as in this case the soil and drainage was 
as good on one line as on the other. Further, there would be some 
saving on the return trip by the shorter road. On the other hand, 
it is probable that the smaller number of acres required for the 
diagonal road would cost at least as much as for the road around 
the quarter-section, owing to the farmers' justifiable disfike for non- 
rectangular fields, and because the diagonal road would divide the 
quarter-section. 

63. There are several matters that materially affect the refia- 
biHty of the method of the above investigation. In the first place, 
the cost of transportation can not be known with any degree of 
refiabihty. The farmers concerned would stoutly contend that the 



DISTANCE 45 



price assumed above is much too great; while freighters would 
claim that it was too low (§ 4-9). 

In the second place, not all of the computed annual saving is 
available for making the improvement, since some of it should be 
set aside to form a sinking fund to be used ultimately in extinguish- 
ing the debt. It is not the part of wisdom to extend the debt very 
far into the future, since the conditions may materially change. 
For example, a new railroad may divert the traffic from this par- 
ticular road, or improvements in the condition of the surface of the 
road may decrease the cost of transportation, — either of which 
would decrease the value of the proposed improvement. Of cour'se, 
certain contingencies may increase the traffic and thereby add to 
the value of the improvement; but it is not wise to incur a definite 
debt for an equal and somewhat problematic saving. Road reformers 
sometimes overlook the fact that interest is a yearly charge and that 
the debt must finally be paid. 

In the third place, the cost of transportation does not necessarily 
vary proportionally to the distance, as was assumed above. If the 
difference in distance is sufficient to make a difference of one trip 
per day, then the value of the saving in distance is tangible; but 
where the saving in length is insufficient for an additional trip, the 
value of the difference in distance depends upon the value, for 
other work, of the small portions of time of men and teams which 
may be saved by the shorter route, — a value which exists, but which 
is difficult to estimate. 

Therefore any estimate as to the value of a saving of distance is 
necessarily only a rough approximation; and at best it should be 
used only as a guide to the judgment. 

64. The problem to find the value of saving distance is very dif- 
ferent for wagon roads than for railroads. In the case of railroads 
the cost of the various elements has been carefully investigated for 
many years, and the transportation is all conducted under a single 
management and by the same party that maintains the road surface ; 
while in the case of wagon roads, a multitude of private parties 
conduct the transportation under various conditions, and the main- 
tenance of the road is in the hands of pubfic officials. 

65. Grade. A level road is most desirable; but as it can 
seldom be obtained, we must investigate the effect of grades upon 
the cost of constructing and operating the road, and also determine 
what is the steepest allowable grade. 

The grade may be reduced (1) by going round the hill or by 



46 ROAD LOCATION [cHAP. M 

zigzagging up the slope, or (2) by cutting down the hill. If the 
slope to be ascended is a long one, the first method must be em- 
ployed; but if the grade is short, the second is usually the cheaper. 
Increasing the length adds to the cost of construction and of trans- 
portation, while cutting down the hill adds only to the cost of con- 
struction. The maintenance of the longer and flatter hne may 
cost either more or less than the shorter and steeper one according 
to the circumstances of the case. In a broken or rough country, 
a proper adjustment of the grades is the most important part of the 
art and science of road building, and the better the road surface the 
more necessary is such an adjustment. 

66. All grades are objectionable for two distinct reasons, viz.: 
because a grade increases the amount of power required to move a 
load up it, and because a grade may be so steep as to Hmit the amount 
of the load that can be moved over the road. The first apj)lies to 
all grades whatever their rate or height; while the latter applies 
only to the steepest grade on the road, and in a measure is inde- 
pendent of its height and depends only on its rate. At present only 
the first objection to grades will be considered; and subsequently 
the second objection will be discussed (§ 74). 

67. Ordinary Effect of Grade. Table 9, page 24, shows the 
load (in terms of the weight of the horse) which a horse with a pull 
equal to one tenth of its weight can draw up various grades on several 
road surfaces. To emphasize the effect of the grade upon the load, 
the same data are presented in a slightly different form in Table 10, 
page 25, which shows at a glance the load on any grade in terms of 
the load on the level. Tables 9 and 10 show that the better the con- 
dition of the road surface, i. e., the less the rolling resistance, the 
more objectionable a grade. For example, according to Table 10, 
on iron rails on a 3 per cent grade a horse can draw only 10 per cent 
as much as on a level; while on a water-bound macadam road on a 
3 per cent grade it can draw 25 per cent as much as on a level. 

A horse can occasionally and for a short time exert a pull equal 
to more than one tenth of its weight. If the grade is not too long, a 
horse can safely exert a force equal to one quarter of its weight, 
and in emergencies one half. 

To move a load over an ordinary earth road requires a tractive 
force of 100 lb. per ton (see Table 8, page 21); and therefore a team 
of 1200-lb. horses exerting a force equal to one tenth of their weight 
can draw 2.4 tons on the level. The reserve power to take the 
load up the hill is (0.25 - 0.10) X 1200 X 2 = 360 pounds. The 



GRADE 47 



total load to be carried up the grade is the wagon and its load plus 
the weight of the team, or 2.4 + (1200 X 2 -^ 2000) = 3.6 tons. The 
grade resistance is 20 lb. per ton for each per cent of inclination 
(§ 23); and the grade resistance for this load on a 1 per cent grade 
is 3.6 X 20 = 72 lb. Therefore, the grade up which a pull of 360 lb. 
will take the 3.6 tons is 360 -^ 72 = 5 per cent, which is the maximum 
permissible grade for an earth road in ordinary condition. The 
team could probably pull this load up 400 to 500 feet of such a grade. 

By the same method of analysis, the load for the same team on a 
level, muddy earth road having a tractive resistance of 200 lb. per 
ton is 1.2 tons, and the maximum permissible grade is 7.5 per cent. 

For a water-bound macadam road having a tractive resistance of 
33 lb. per ton, the load on the level is 7.3 tons, and the permissible 
maximum grade is 2.2 per cent. 

68. What load can the above team take up a 4 per cent maxi- 
mum grade on a water-bound macadam road having a tractive 
resistance of 33 lb. per ton? The grade resistance is 20 X 4 = 80 lb. 
per ton; and the tractive resistance is 33 lb. per ton; therefore the 
total resistance is 80 + 33 = 113 lb. per ton. The maximum tractive 
power of the team is equal to one quarter of its weight, or 600 lb.; 
and the grade resistance for the weight of the team = 2400 -^ 2000 X 
80 = 96 lb. ; therefore the net tractive power of the team is 600 — 
96 = 504 lb. Then the weight of the wagon and the load which the 
team can draw up this grade is 504 -^ 113 = 4.4 tons. 

69. Rise and Fall. By rise and fall is meant the vertical height 
through which the load must be lifted in passing over the road in each 
direction. One foot of rise and fall is a foot of ascent with its cor- 
responding foot of descent. In passing over a ridge 10 feet high 
standing in the middle of a level plain, there is only 10 feet of rise 
and fall; and not 10 feet of rise plus 10 feet of fall. If the road is 
level. Fig. 4, then an elevation or depression of, say^ 1 foot produces 



Fig. 4. Fig. 5. 

literally 1 foot of rise and a corresponding foot of fall; but if the 
road is on a steep grade, Fig. 5, an elevation of 1 foot above the grade 
line or of a Hke amount below the grade line, literally speaking, 
produces no rise and fall, because in either case it is a continuous 



48 ROAD LOCATION [CHAP. II 

up grade. However, as far as operation is concerned, the two 
cases are exactly alike, and each has a foot of rise and fall. 

Rise and fall is measured by the number of vertical feet of rise, 
as shown by the differences of elevation on the profile. 

70. The introduction of rise and fall is a question either (1) 
between the increased cost of operation and the increased cost of 
construction required to fill up the hollow or to cut down the hill, 
or (2) between the cost of operation of the rise and fall and of the 
increased distance necessary to go around the obstruction. 

The following example is often cited as showing the improve- 
ment that can be made in locating roads. ^' An old road in Anglesea 
rose and fell between its extremities, 24 miles apart, a total vertical 
amount of 3,540 feet; while a new road laid out by Telford between 
the same points, rose and fell only 2,257 feet; so that 1,283 feet of 
vertical height is now done away with, which every horse passing 
over the road had previously been obliged to ascend and descend 
with its load. The new road is, besides, more than two miles shorter. 
Such is one of the results of the labors of a skilful road maker." 
The road may have been economically re-located, but the citation 
fails to show whether the increased cost of construction to eHminate 
rise and fall was justified by the decreased cost of operation. 

The following example from the same author, also frequently 
quoted, shows that rise and fall was ehminated by increasing the 
distance, although no attempt is made to show that the increased 
distance was more economical than the rise and fall thereby elimi- 
nated. " A plank road, laid out between Cazenovia and Chitten- 
ango, N. Y., is an excellent exemplification of the true principles of 
road making. Both these villages are situated on the Chittenango 
Creek, the former being 800 feet higher than the latter. The most 
level wagon road between these villages rises more than 1,200 feet in 
going from Chittenango to Cazenovia, and rises more than 400 feet in 
going from Cazenovia to Chittenango, in spite of this latter place 
being 800 feet lower. It thus adds one half to the ascent and labor 
going in one direction; and in the other direction it goes up hiU one 
half the height, which should have been a continuous descent. The 
line of the plank road by following the creek (crossing it five times) 
ascends only the necessary 800 feet in one direction, and has no 
ascents in the other, with two or three trifling exceptions of a few 
feet in all, admitted in order to save expense. There is a nearly 
vertical fall in the creek of 140 feet. To overcome this, it was 
necessary to commence far below the falls, to cHmb up the steep 



RISE AND FALL 49 



hillside, following up the sides of the lateral ravines until they were 
narrow enough to bridge, and then turning and following back the 
opposite sides till the main valley was again reached. The extreme 
rise is at the rate of 1 foot to the rod (1 in 16j), and this only for 
short distances, and in only three instances, with a much less grade 
or a level intervening." 

71. Classes of Rise and Fall. In discussing the effect of rise and 
fall upon the operation of a road, a distinction must be made be- 
tween three classes of rise and fall, as follows: 

Class A. Rise and fall on grades at a less slope than the angle 
of repose (the grade on which a vehicle by its own weight will main- 
tain a uniform speed), and so situated as not to require any addition 
to the total power required to move a load over the road. 

Class B. Rise and fall on grades so steep as to require either the 
holding back of the load by the team or the application of brakes. 

Class C. Rise and fall on the maximum grade. 

72. An example of the first class of rise and fall is shown in 
Fig. 6. The team is reheved on the down grade an amount exactly 

equal to the extra tax upon the up __^ ^ -^ 

grade, and the only effect upon the ^^"^^ 

team is that the effort is concentrated ^^^' ^' 

on the up grade instead of being uniformly distributed over the road; 
but as the slope is assumed to be equal to or less than the angle of 
repose, the maximum effort is equal to or less than twice the normal. 
If the grade hne rises above the level instead of dipping below it, 
the case is not changed except that the rise is a little more unfavor- 
able, since the team has no relief before the increase in effort is 
required. Therefore this class of rise and fall costs little or nothing. 

In the preceding examples, a change of velocity would alter the 
power required at any particular instant; but in wagon-road traffic 
the speed is always small and consequently the effect of variations 
of speed are quite small, and may be entirely neglected. On rail- 
roads a variation of the velocity materially affects the cost of rise 
and fall. 

If the grade is greater than the angle of repose, the team in descend- 
ing must hold back the load, which is lost energy, or brakes must 
be appUed, which tend to destroy the road; and in ascending, the 
demand upon the team is greater than twice the normal. There- 
fore in either case this class of rise and fall adds to the cost of oper- 
ating the road. 

If the grade is the maximum, it may be sufficient to Hmit the 



50 ROAD LOCATION [CHAP. II 

amount of the load a team may draw over the more level portions 
of the road, and therefore greatly add to the cost of transportation. 
As a chain is no stronger than its weakest link, so a road is no better 
than its steepest grade. 

73. Cost of Rise and Fall. What does it cost to develop the 
power required to haul a load up a grade less than the grade of 
repose? In other words, what is the cost of Class A rise and fall? 

The cost of transportation consists chiefly of the cost of driving, 
of feed, and of the wear and tear on the team. Usually the cost of 
driving will be approximately half of the total cost of transportation; 
and as a team can draw a load up the grade of repose at practically 
the same speed, at least for short stretches, as upon the level, there 
will usually be no material incraase in the cost of driving. Even 
though the team may travel slower because of the grade, the cost 
of the increased time can scarcely be computed because of the impos- 
sibihty of determining the value of fractions of time for other pur- 
poses. The cost of wear and tear on the team and part of the cost of 
feed must vary approximately as the total power developed. There- 
fore the conclusion may be drawn that rise and fall belonging to 
Class A will not add appreciably to the cost of transportation. 
This conclusion is corroborated by the popular behef that a gently 
undulating road is less fatiguing to horses than one which is perfectly 
level. The argument in support of this belief is that alternations of 
ascents, descents, and levels call into play different muscles, allowing 
some to rest while others are exerted, and thus reHeving each in turn. 
The argument is false, and probably originated in the prejudices of 
man in his quest for variety, rather than in the anatomy of the horse; 
but the above theory would not have gained its wide popularity 
if a gently undulating road were appreciably more fatiguing to a 
horse than a perfectly level one. A perfectly level road is the best 
for ease of transportation. 

74. Limiting Effect of a Grade. If the grade is steeper or longer 
than that up which the team can draw the normal load by exerting 
twice the tractive power required on the level, i. e., if the rise and fall 
belongs to Class C, then the grade has the effect of limiting the load 
that can be drawn over the level portion of the road, and conse- 
quently increases the cost of transportation. The load which a team 
can draw up any grade can be approximately computed as in § 68. 
If the load that can be drawn up any particular grade is, for example, 
three fourths of the normal load on the level; then it will cost as much 
to haul three fourths of a load with this grade as a full load without 



■ 



RISE AND FALL 51 



the grade. If the cost with a grade less than the maximum is 10 
cents per ton-mile (§ 4-7 and § 12), then the cost with the maximmn 
grade will be 10 -^ f = 13 J cents per ton-mile; and therefore for 
each ton going over the road, the maximmn grade adds 3j cents per 
ton mile. In determining the amount of traffic, only full loads 
should be included; but notice that the full load varies with the 
speed. A ton may be a full load at 3 miles per hour, while half a 
ton may be a full load at 6 miles per hour. 

Knowing the load on the maximum grade and also the cost per 
ton-mile for a level road or for a grade less than the maximum, the 
justifiable expenditure to reduce the maximum grade may be com- 
puted as follows: The difference in cost per ton-mile with and with- 
out the maximum grade may be determined as in the preceding 
paragraph; and this multiplied by the number of loads annually 
going over the road gives the sum that may be spent annually to 
reduce the maximum grade to the lesser value. This sum may be 
used to pay interest on the cost of cutting down the hill or of filling 
up the hollow. 

The data are so uncertain that the result must be regarded only 
as a rough approximation; and yet it is worth while to make an 
investigation as above as a guide to the judgment. 

75. Class B rise and fall is intermediate between Class A and 
Class C, and its cost is even more difficult to compute than that of 
Class C. The chief difficulty is in determining the relative cost of 
developing power on a level and up a grade. Only an estimate can 
be made, and the estimate will vary greatly with the point of view. 
For example, farmers usually have a surplus of power (horses) as 
far as transportation is concerned, and therefore they would con- 
sider a slight increase in the demand for power as a matter of small 
moment. Again, teamsters differ greatly as to what is a proper 
or economical load for a horse, and also as to the effect of a tem- 
porary over-load. 

There are two methods of computing the cost of this class of 
rise and fall, neither of which is more than roughly approximate. 

1. Assume that the cost of Class B rise and fall bears the same 
relation to that of Classes A and C, that the grade of B bears to that 
of A and C. Then if the grade for Class B is only a fit tie greater 
than the angle of repose, the cost is only a trifle greater than that 
of Class A; and if the grade is nearly a maximum, then the cost of 
the rise and fall closely approximates that of Class C. 

2. Assume that the energy developed on a grade over and above 



52 ROAD LOCATION [CHAP. II 

ehat required on the grade of repose, costs the same per unit as that 
of an equal amount of energy developed on the level. For example, 
assume that the rise is 1 foot more than the angle of repose; and 
assume that the cost of drawing a load on a good water-bound 
macadam road is 5 cents per ton-mile (§ 5-6), and that the tractive 
power is 40 lb. per ton. Then, moving a ton 1 mile will develop 
5,280 X 40 = 211,200 foot-pounds of energy, which will cost 5 cents. 
The cost of 1 foot-pound of energy, then, is 5 -^ 211,200 = 0.000,023,7 
cents. Drawing a ton over a rise 1 foot high develops 2,000 foot- 
pounds, the cost of which is 0.000,023,7 -^ 2 X 2,000 = 0.023,7 
cents. In going up the above grade, the team must develop enough 
power to move the load up the grade of repose and in addition must 
develop enough to Hft the load 1 foot vertically. Therefore the 
cost of the 1 foot of rise assumed above is 0.023,7 cents for each 
ton going over the road. 

It was assumed above that the load is retarded in the descent by 
the application of brakes; but if the grade in question is situated in 
a flat country where brakes are not usually placed upon vehicles, 
the team must hold back on the descent an amount equal to the 
extra energy required on the ascent, and therefore the cost of the 
foot of rise and faU will be, almost or quite, doubled. 

With data similar to the above, and with a knowledge of the 
amount of traffic, it is a simple arithmetical process to compute the 
sum that may be spent annually to eliminate one or more feet of 
rise and fall. Notice that in this case only the full loads should be 
considered (see the first paragraph of § 74). For example, assume 
that a water-bound macadam road has a traffic of 20 tons per day 
one way for 300 days of the year, or an annual traffic of 20 X 300 
= 6,000 tons. The cost of a foot of rise and fall per ton of traffic 
is 0.023,7 cents, and the annual cost on this particular road is 0.000,237 
X 6,000 = $1.42. This is the amount which, according to the above 
investigation, can be spent annually to cut down the hill or to fill 
up the hollow sufficiently to eliminate 1 foot of rise and fall. 

Similarly, for an earth road having a cost of 15 cents per ton- 
mile and a tractive power of 100 lb. per ton, 1 foot of rise costs 
0.028,4 cents, and the foot of ascent assumed above will cost 0.028,4 
cents for each ton going over the road. If this road has a traffic 
of 5 tons one way for 300 days of the year, the annual cost of the 
foot of rise and fall is 0.028,4 X 5 X 300 = 44.6 cents, which is 
the sum that can be spent annually to eliminate the foot of rise and 
fall. 



RISE AND FALL 53 



From the point of view of the last solution, it appears that the 
cost of Class A rise and fall increases with the steepness of the 
grade, that is, increases as the rate of the grade approaches the 
angle of repose. In all probabihty this is correct, but all the data 
involved are too uncertain to warrant any further discussion of 
the subject here. However, the engineer should bear such relations 
in mind in solving a particular problem. 

76. Distance vs. Rise and Fall. In locating a road the question 
may arise between the relative desirabihty of introducing rise and 
fall and of increasing the length of the road. The problem then is 
to determine the relative value of distance and of rise and fall. 

If the conclusion in § 73 is correct, that the cost of Class A rise 
and fall is not appreciable, then the distance should not be increased 
at all to ehminate Class A rise and fall. 

77. For Class B rise and fall an approximate solution can be 
obtained by assuming that it costs the same to develop a certain 
amount of energy in overcoming Class B rise and fall as to develop 
a like amount of energy in moving a load on a level road. This 
assumption is probably reasonably correct. 

For example, the tractive resistance of the best water-bound 
macadam road is 33 lb. per ton, and the work necessary to raise 1 ton 
through 1 foot of rise is 2,000 foot-pounds; therefore to develop 
2,000 foot-pounds of work on a level water-bound macadam road, 
a ton must be moved 2,000 -^ 33 = 60 feet. Hence the cost of 
operating 60 feet of distance on this road may be considered as equiv- 
alent to 1 foot of rise and fall. Therefore to eliminate a foot of rise 
and fall of Class B, the length of the road may be increased 60 feet. 
Table 14 gives the corresponding distance for other road surfaces.* 

78. Apparently writers on roads have not made a distinction 
between the several classes of rise and fall. Herschel says: t "To 
determine whether it is more advisable to go over than around a 
hill, all other considerations being equal, we have this rule: Call the 
difference between the distance around on a level and that over the 
hill d (the distance around being taken as the greater), and call h 

* The above relations are for a load transported on wheels. It may be interesting to know 
the corresponding relations for pedestrians. The work (energy) required of a man in walking 
is practically independent of the nature of the road surface. A man makes progress in walking 
by allowing his body to fall through a small space and then raising it again preparatory to 
another fall. For an average man, the energy expended in walking 16 to 20 feet horizontally 
is sufficient to raise his body through 1 foot vertically. Therefore, for pedestrians 1 foot of 
rise and fall is equivalent to, say, 18 feet of horizontal distance. 

t Clemens Herschel, Science of Road IMaking, Prize Essay of the State Board of Agriculture 
of Massachusetts, Boston, 1869, p. 207-63; revised edition, Engineering News, New York, 
1890, p. 9. 



54 



KOAD LOCATION 



[chap. II 



TABLE 14 

Horizontal Distance Equivalent to 1 Foot of Class B Rise and Fall 
Earth roads, muddy (tractive resistance 200 lb. per ton) .... 10 feet 



' ' ordinary 

' ' dry and hard 

Stone-block pavement, best 

' " " ordinary 

Gravel, best 

' * ordinary 

Water-bound macadam road, best .... 
" " " ordinary 

Brick on concrete 

Sheet asphalt 

Iron rails, clean 



LOO 




. 20 '' 


80 




. 25 '' 


40 




. 50 " 


80 




. 25 " 


50 




. 40 " 


80 




. 25 '' 


33 




..60 " 


50 




. 40 '' 


25 




. 80 '' 


20 




. 100 '' 


10 




. 200 '' 



the height of the hill. Then in case of a first-class road, we go round 
when d is less than 16/i; and in case of a second-class road, we go 
round when d is less than lO/i." Although not specially so stated, 
the above rule was plainly intended for water-bound macadam 
roads. 

The above rule (which has been frequently quoted) recognizes 
no distinction between the several classes of rise and fall. It makes 
the avoidance of a foot of rise in going over a small culvert or of a 
foot of fall in crossing an open ditch, equally as important as the 
elimination of a foot of rise and fall on the maximum grade. It is 
not possible to draw sharp hnes between the several classes of rise 
and fall, but it is certain that there is a great difference in cost 
between a foot of rise and fall on a flat grade and the same quantity 
on the maximum or Umiting grade. Notice that the above rule 
makes the horizontal distance equivalent to a foot of rise much less 
than that stated in Table 14. 

79. Maximum Grade. The fixing of the proper maximum or 
ruling grade is the most important matter connected with the loca- 
tion of a road. To do this intelUgently, the maximum grade must be 
considered both as an ascent and as a descent. Viewed as an 
ascent, the maximum or ruUng grade chiefly concerns the draught of 
heavy loads; and viewed as a descent, it chiefly concerns the safety 
of rapid traveling. In both respects, the effect of the grade in 
limiting the load depends upon its rate, and is practically inde- 
pendent of its length. 

80. As an Ascent. The load which a team can draw over any 
road is determined by the length and steepness of the maximum 
grade; or, in other words, the length and rate of the permissible 



MAXIMUM GRADE 55 



maximum grade depends upon the endurance of the team. Th. 
method of computing the load that a team can draw up any grade 
was explained in § 68, page 47. That investigation shows that the 
permissible maximum grade varies greatly with the conditions of 
the surface; and that the better the surface the less should be the 
ruUng grade. In other words, unless the maximum grade is light, 
the amount that can be hauled on a water-bound macadam road 
does not differ greatly from that on an earth road. 

A team could probably pull the maximum load up a stretch 
of the maximum grade 400 to 500 feet long; and if the maximum 
grade does not occur too often, it could probably pull the load up a 
stretch two or three times as long. On long maximum 'grades, it is 
wise to provide a little stretch of nearly level grade upon which to 
let the team rest. In the above computation, the team is assumed 
to have a reserve power equal to that exerted on the maximum 
grade; but the power required to start the load may be four or 
five times the normal tractive resistance, and hence a nearly level 
resting place is required, so that the team may readily start the 
load. 

81. Many books on roads state that if the maximum grade 
is long, the slope should be flattened toward the simimit to com- 
pensate for the decreased strength of the fatigued horses. This 
reasoning is incorrect and the remedy is impracticable. The argu- 
ment is incorrect since it assumes that if the horse is to develop 
energy to lift the load up the incHne, it should not work at a uniform 
rate. Universally the race horse goes fastest on the home stretch; 
and if it is urged to its utmost speed at first, it is sure to lose the race. 
The reconmtiendation is impracticable, since the topography would 
rarely permit the flattening of the grade at the top without increased 
expense, and it would not be wise to incur extra cost for this pu:- 
pose. 

82. If the loads are much heavier in one direction than in the 
other, it is permissible to oppose the lighter traffic with the steeper 
ruling grade. 

83. As a Descent. Viewed as a descent, the maximum grade 
concerns chiefly the safety of rapid travel. Many writers on roads 
claim that the descending grade should not exceed the angle of 
repose, i. e., should not exceed the inclination down which the 
vehicle will descend by its own weight. This limit is impracti- 
cable, since the angle of repose varies with the kind of vehicle, 
degree of lubrication, amount of load, size of wheels, etc. Besides, 



56 ROAD LOCATION [cHAP. 11 

this limitation is unnecessary, since the resistance of traction in- 
creases as the speed, and in going down it is only necessary to 
drive faster to prevent the vehicle from unduly crowding upon 
the team; but of course this remedy has its limitations. Further, 
the speed in descending may be checked by the application of the 
brake; but it should be remembered that the use of the brake is 
detrimental to the road surface, particularly on the maximum 
grade. 

Grades twice as steep as the angle of repose are Operated without 
inconvenience or danger. In Europe it is usually assumed that on a 
good water-bound macadam road, of which the angle of repose is 
about 2 or 2 J per cent, a 5 per cent grade is the maximum that can 
be descended safely at a trot without brakes; and, if the stretch 
is long, 3 per cent is considered the maximum for safety. On moun- 
tain roads having a water-bound macadam surface, freight wagons 
descend 12 per cent grades by the use of brakes, but only with 
expert drivers. 

84. Safety at Siimmit. The grade each side of the summit 
should be such that two automobiles approaching the summit should 
be able to see each other when at least 200 feet apart, which is prac- 
tically equivalent to limiting the grade for 100 feet on each side of 
the summit to 5 per cent, or in other words to limiting the simi of 
the grade for 100 feet either side of the sunmiit to 10 per cent. This 
is particularly important on a road having only a one-track improved 
surface. 

Where a highway crosses a steam or electric railway on the same 
level, and where the highway has a steep grade as it approaches the 
crossing, there should be sufficient level road at the top of the grade, 
say 50 feet, to permit a wagon or an automobile, particularly the 
latter, to stand while the train passes. If this condition does not 
obtain, an automobilist is liable to kill his engine at the top of the 
grade just as he is starting to cross the track and just as a train is 
coming. Automobilists quite frequently encounter such dangerous 
crossings. 

The crossing should be wide enough, say 18 feet, to permit two 
vehicles to meet upon the crossing. 

85. Table 15, page 57, are the limits reconunended by a special 
committee of the American Society of Civil Engineers.* They are 
presented here for convenience of reference and comparison. 

* Proc. Amer. Soc. of C. E., Vol. 42 (1916), p. 1612. 



MAXIMUM GRADE 57 



TABLE 15 
Maximum Permissible Grade 



Kind of Road Surface. 



Stone block with bituminous filler 

Gravel 

Brick with bituminous filler 

Water-bound macadam 

Stone block with portland-cement filler 

Bituminous macadam 

Bituminous concrete 

Portland-cement concrete 

Bituminous carpet 

Brick with portland-cement filler 

Sheet asphalt 

Wook block 



Grade. 



15 

12 

12 

12 

9 

8 

8 

8 

6 

6 

5 

4 



86. Minimum Grade. Considering only the cost of transporta- 
tion, a perfectly level road is the best; but it costs less to maintain 
a road upon a slight grade than one perfectly level. All roads 
should be higher in the center than at the sides, so as to shed the 
rain to the side ditches, but on any road longitudinal ruts are lia- 
ble to form and interfere with the surface drainage ; and therefore if 
the road is perfectly level in its longitudinal direction, its surface 
can not be kept free from water without giving it so great an incli- 
nation transversely as to expose vehicles to the danger of overturn- 
ing or skidding. On a perfectly level road, every rut will hold water, 
which will soak into the road and soften it whether it be earth or 
broken stone; whereas with even a slight longitudinal grade, every 
wheel track becomes a channel to carry off the water. It is a com- 
mon observation that earth roads running up hill and down dale 
have surfaces better to travel upon than more level ones. This is 
largely due to the better longitudinal surface drainage. 

The harder the road material the less the necessity for longitudi- 
nal drainage of the surface. An earth road surface is certain to 
wear into ruts, and hence is greatly benefited by having a longi- 
tudinal slope. Gravel and broken-stone roads are liable to wear 
into longitudinal ruts, and hence need longitudinal drainage. Water- 
bound macadam roads built with the hardest limestones or trap are 
not easily worn into ruts, and therefore the necessity for a longi- 
tudinal grade is less with this class of construction. 

A longitudinal grade decreases the cost of maintenance, and the 
advisability of introducing a grade for such a purpose depends upon 
the relative cost of constructing it and upon the capitaHzed value 



58 ROAD LOCATION [CHAP. II 

of the cost of maintaining it. With earth roads the expenditures 
for maintenance are ordinarily too slight to justify much expense in 
securing a longitudinal grade; but with high class broken-stone 
roads, which naturally have a heavy traffic, a considerable expense 
to secure a sHght longitudinal grade is usually justifiable. Engi- 
neers whose experience has been largely upon railroads and canals 
are prone to spend money to secure an absolutely level road, where 
a sUght grade could be secured at less expense. In filling up a 
hollow or cutting down a hill, the employment of a light longitudinal 
grade may decrease the cost of construction and also the cost of 
maintenance without increasing the cost of transportation (§ 71-73). 
The important principle to remember is that a slight longitudinal 
grade is an advantage; although over a long stretch of level country 
it may not be practicable to secure it. 

The following is the minimum grade adopted by leading engi- 
neers for water-bound macadam roads: in England 1 in 80 or 1 J 
per cent; in France, by the Corps des Fonts et Chaussees, 1 in 125 
or 0.8 per cent; in the United States 1 in 200 or 0.5 per cent. 

87. Curves. Theoretically the shortest radius of curvature 
allowable on roads depends upon the width of the road, and upon the 
maximum length of horse teams frequenting the road or upon the 
speed of the shorter teams. Since the length of a four-horse team and 
vehicle is about 50 feet, to permit such a team to keep upon a 12-foot 
roadway would require a radius of the inside of the ciu-ve of about 
100 feet; on a 16-foot roadway a radius of about 75 feet would be 
required; and on an 18-foot roadway, a radius of about 66 feet. 
In France the minimum radius is as follows: on main and depart- 
mental roads of which the trackway is 20 to 22 feet wide, 165, and 
in extreme cases 100 feet; on principal country roads which are 
20 feet wide, 50, In Saxony the minimum radius on principal roads 
is 82 feet, and on ordinary country roads it is 40 feet. 

" On mountain roads with grades of 1 or 2 per cent, heavy teams 
require curves of 40 feet radius, and light ones 30 feet; and with 
grades of 3 or 4 per cent, heavy teams require 65 and light ones 50 
feet." " In extreme cases on mountain roads four- and six-horse 
teams haul maximum loads over 16-foot roads having a radius at 
their outer edge of 30 feet." However, in this case the roads on 
the curves must be level, as the rear team is expected to do all of 
the pulling on the ciu*ve. 

88. For safety of automobile travel, curves should be so flat 
that two automobiles in approaching will be able to see each other 



CURVES 



59 



when at least 200 feet apart; and where this is not feasible, a con- 
spicuous sign should be placed. When the curve is located on a grade, 
the radius of the curve should be not less than 300 or 400 feet, even 
if the view is unobstructed. 

At the corners or intersections of roads, the hedges, trees, etc., 
should be removed so that automobilists approaching the corner 
can have an unobstructed view of the side road for 200 or 300 
feet. 

89. 90° Curves. There are many 90° curves in highways, 
especially in that part of the country where the land was survej^ed 
according to the U. S. pubUc land system. If a pavement 15 feet 
wide is constructed in 
the middle of a 50-foot 
right-of-way, and if the 
improvement is to be 
kept within the right-of- 
way at the corner, the 'Righft^ 
radius of the center Une 
of the curve can be only 
52.9 feet. But by pur- 
chasing a comparatively 
small area on the corner, 
the length of the radius 
can be greatly increased. 
Fig. 7 shows a solution 
of this problem.* '' The 
piece of land L K M N 
contains only 0.055 acres, 
and often the saving in 

the decreased amount of paving will more than pay for the extra 
land. In addition the right-of-way is not contracted at the corner 
as it is by the shorter radius curve, so that the 17.5-foot margin 
between the inner edge of the pavement and the proper tyline is pre- 
served for use as an earth road around the corner as well as on tan- 
gents." 

Fig. 8, page 60, shows the solution of the above problem at the 
intersection of two paved roads, t " Sections like GHJKLPQR 




Fig. 7. — Curve of Paved Way at 90° Corner. 



* H. E. Bilger, Road Engineer, Illinois Highway Department, Illinois Highways, January, 
1917, p. 5. 

t H. E. Bilger, Road Engineer, Illinois Highway Department, in Engineering News- 
Record, Vol. 79 (1917), p. 134. 



60 



ROAD LOCATION 



CHAP. II 



should be built monolithic with the usual convexity of surface at 
JK, although J is depressed. Areas like HJK will come out warped 
surfaces, but are easily built by an experienced contractor. The 




Fig. 8. — Curves at Inter^vSCTion of Two Paved Roads. 



ten construction joints shown should be nothing more than planes 
of cleavage. Sections like KEF J, which are built last, have their 
corner elevations fixed by the main pavement. Therefore the usual 
convexity of surface is preserved ; and the inner edge FJ is depressed 
to meet the required elevation. In areas like KLE the surface of 
the ground should be kept about 1 inch below that of the surface 
of the pavement adjacent. The catch basins and drains will keep 
the ground dry." 

90. Super-elevation. It is natural for vehicles to keep to the 
inside of the curve, partly to save distance and partly to get the 
benefit of the crown of the road to prevent tipping outward. If 
the curve has no super-elevation on the outside, the slew of the 
vehicle, particularly a fast-moving motor-driven one, will materially 
grind out the surface of the road. 

The theoretically perfect super-elevation is given by the formula 



E 



32.2 R 



(1) 



CURVES 61 



in which E is the elevation in feet, W the width of the road in feet, 
S the speed in miles per hour, R the radius of the curve in feet. 
However, the maximum super-elevation is Hmited by the transverse 
slope suitable for horse-drawn traffic. 

The method adopted by the lUinois Highway Department is 
very simple and effective. It is as follows: "Whatever the char- 
acter of the road surface, the inner half of the curve is carried around 
on the level; and the outer half of the curved roadway is elevated 
so that the surface is a right line from inside to outside on any 
radial line. For example, if the road surface is concrete 16 feet wide 
with a 2-inch crown, then the outer edge of the outer half will be 
elevated 2 inches, and the super-elevation of the curve proper will be 
4 inches; and including the slope of the extra width (§97), the total 
super-elevation will be nearly 5 inches." 

The California Highway Department employs the following 
method : The super-elevation on all curves is f inch per foot, which 
on a 300-foot radius is perfect compensation for a speed of 17 miles 
per hour and on a 200-foot radius for 13 miles per hour. 

When curves have the proper super-elevation, the tendency 
to keep to the inside of the curve will be less, and the damage due 
to slewing will be nearly or wholly eliminated. For the best results 
the super-elevation should begin a short distance before the tangent 
point and not reach its full amount until an equal distance past the 
tangent point. 

91. Aesthetic Value of Curves. On a curved road there is a 
constantly changing panorama or vista before the traveler, rather 
than the constant and uninteresting vanishing point on a straight 
road. However, in most cases the location of buildings and the tillage 
of fields have fixed the location of the road within narrow limits ; and 
hence there is but little opportunity to consider the aesthetic or 
artistic features of the location of the ordinary highway. In the loca- 
tion of park drives the artistic feature is the controlling element. 

92. Width. Under this head will be considered the width of 
the right-of-way and also the width of the improved portion. 

93. Width of Right-of-Way. The legal width of right-of-way 
varies greatly in different states. In an early day, before any attempt 
was made to improve the wheelway, the legal width was often 100 
feet, and sometimes 10 rods (165 feet). In some of the states where 
land is cheap, the former width to some extent still prevails. In 
most of the states of the Mississippi Valley, particularly those in 
which the land was divided according to the system of U. S. pubUc 



62 ROAD LOCATION [CHAP. II 

land survey, the legal width of right-of-way is usually 66 feet. A 
few of these states classify the roads, making the less frequented 
ones narrower ; for example, in Texas the widths of first, second, and 
third class roads are 60, 30, and 20 feet, respectively. In the earher 
settled states along the Atlantic coast, 3 rods (49i feet) is a common 
width, although some of the less frequented roads are only 2 rods 
(33 feet) wide. 

If the surface is loam or clay, a considerable width of traveled 
way is required that the traffic may not cut the surface up so badly 
when it is soft. This is probably the explanation of the 60 or 66 
feet so common in the Mississippi Valley. In some of the states, 
for example, IlHnois, the law specifies that, '' if possible," a strip 
equal in width to one tenth of the right-of-way shall be reserved for 
pedestrians on each side between the property fine and the ditch. 
This leaves 53 feet for the wheelway and ditches, which is probably 
none too much for a loam or clay road. If the ditches are deep and 
consequently wide, the sidewalk is usually curtailed rather than the 
wheelway. 

In Massachusetts the roads improved by state aid usually have a 
right-of-way of 50 feet wide, and in localities where there was a 
possibiHty of space being required by an electric road, they are 60 
feet, the latter being considered sufficient to accommodate a double- 
track electric road, wagon ways, and sidewalks. 

94. In England the principal roads, especially those near popu- 
lous cities, are laid out 66 feet wide, 20 or 22 feet being covered 
with broken stone. 

In Holland the usual width is 38 feet, of which 14 feet is 
improved. 

In France the standard widths are to the nearest foot as follows: 

Class of Road. Right-of-Way. Width Improved. 

National roads 66 feet 22 feet 

Departmental roads 40 " 20 " 

Provincial " 33 " 20 " 

Neighborhood " 26 '' 16 " 

95. Width of Improved Portion. In view of the cost of improv- 
ing or paving the roadway, it is important to determine the proper 
or best width of the improved portion. The best or economic width 
of the improved portion depends upon (1) the cost of the paved 
portion, (2) the cost of constructing the shoulders, i. e., of partially 
improving or hardening the natural soil at the edges of the improved 



WiDtH 63 



portion, (3) the amount of travel, and (4) the proportion of motor- 
driven vehicles. 

Except for cost, the wider the improved way the better; but length 
is more valuable than width, and it is often difficult to get an improved 
road because of the expense. Hence it is wise to make the paved way- 
only wide enough to accommodate the travel reasonably well. 

The width necessary for ordinary rural traffic is often over- 
estimated. Two wagons having a width of wheel base of 5 feet and 
a width of load of 9 feet can pass on a 16-foot roadway and leave 
6 inches between the outer wheel and the edge of the paved way 
and a clearance of 1 foot between the inner edges of the loads. This 
extreme case will rarely occur, and hence a width of 16 feet will 
certainly be enough unless there is considerable rapid traffic. 

The Massachusetts Highway Commission carefully measured 
the width of traveled way on numerous crushed-stone roads, and 
found that with an improved width of 15 to 24 feet,^the average 
being 16.1 feet, — the maximum width of traveled way averaged 
14.92 feet and the width commonly traveled averaged 11.05 feet.* 
On this evidence the Commission concludes that " a width of 15 
feet is ample except in the vicinity of the larger towns, and that 
12 feet is sufficient for the fighter traveled ways, bat that 10 feet 
is too narrow unless good gravel can be obtained for the shoulders.'' 
The average width conmionly traveled on forty-six of the 15-foot 
roads was 9.58 feet. 

In New Jersey the improved width for state-aid roads is 9 to 
16 feet, mostly 10 to 12 feet. The improved width of French roads 
varies from 16 to 22 feet (§ 94) ; in Austria, from 14 to 26 feet; and 
in Belgium there are many roads surfaced only 8 J feet wide. 

96. The preceding data for the width of the improved portion.were 
fixed before automobiles became numerous. NaturaUy provision 
should be made to permit automobiles to pass safely at considerable 
speed ; and hence the widths stated above are too small. Two auto- 
mobiles can not safely pass at low speed upon less than 12 feet, and 
usually it is considered that a road having any considerable motor 
travel should have a width of 14 or 16 feet. The Massachusetts 
Highway Conmiission once built double-track roads 18 feet wide; 
but in consideration of the large number of wheels that went off 
the side of the improved way, increased the width to 19i feet, after 
which few, if any, wheels went off the side. 

* Report of the Massachusetts Highway Commission for 1897, p. 31. For a summary of 
similar data for each township for five years, see Report for 1901, p. 47-55. 



64 ROAD LOCATION [CHAP. H 

97. Width on Curves. If the deflection angle is more than about 
30°, the traveled way should be widened on the curve. If there is 
Hkely to be much motor-driven traffic, the width at the center of the 
curve should be increased 30 to 40 per cent, the increase tapering 
to nothing at the tangent points. 

The slope of the inner half of the curve should be continued over 
this extra width. 

If the improved way is so narrow that a considerable number 
of vehicles turn off upon the shoulders, then the proper construction 
of the shoulders becomes a considerable item; and it may be wiser 
to improve a wider portion and spend less money upon the shoulders. 
Obviously the best width depends upon the amount of travel, the 
relative cost of the pavement and of improving the shoulders. It 
has been said that if a vehicle is compelled to turn off on the 
shoulder more than five times in going a mile, the improved portion 
should be widened. 

Since earth roads have the same material in the shoulders as in 
the traveled way, and since the cost of an improved earth road is so 
small, the whole width between the side ditches should be unproved. 
Since gravel roads are comparatively cheap to construct, and since 
there is only a httle difference between the cost of the improved way 
and that of the shoulders, gravel roads can appropriately be wider 
than roads of higher unit cost. For current practice concerning the 
width of gravel roads, see Figs. 44 and 45, page 170. For examples 
of the way in which these principles have been applied in water- 
bound macadam, see Figs. 48-56, pages 197-99; and for concrete 
roads, see Fig. 75, page 243. 

98. Location of the Wheelway. The improved portion is some- 
times placed in the middle of the traveled way, and sometimes at 
one side. Apparently the natural position is in the middle with an 
earth track on each side; but in this case, if the pavement is crowned, 
as is usual, one half of the storm water faUing on it is discharged 
upon the shoulder at each side of the pavement, i. e., upon that por- 
tion of the road the harder to keep in proper condition. On the 
other hand, if the improved portion is placed at one side of the trav- 
eled way, and if at the same time it is given a uniform slope toward 
the nearer side ditch, all of the storm water faUing upon the im- 
proved portion will be discharged upon the unused shoulder next to 
the side ditch and therefore do no harm. Further, in many cases 
grass wiU grow upon the unused shoulder and protect it, so no harm 
will be done if an occasional wheel does turn off onto this shoulder. 



PLACING THE LINE 



65 



The heavier loads usually go toward town; and therefore if 
the single-track improved portion is placed upon the right-hand side 
going toward town, the heavier loads will have the right-of-way (in 
the United States at least), and will not turn off from the paved 
portion. 

99. CROSS Section. The cross section of a road or pavement 
depends upon the material of the road surface, and hence will be 
considered in the respective chapters following. 

However, the data in Table 16 on the crown or transverse slope 
of the road surface are given here for convenience of reference and 
comparison. These values were recommended by a special com- 
mittee of the American Society of Civil Engineers. * 

TABLE 16 
Crown of Roadway 



Material of Roadway. 



Transverse Slope, 
Inches per Foot. 



Maximum. 



Minimum. 



Earth 

Gravel 

Water-bound Macadam . 

Bituminous Macadam ... 

Bituminous Concrete 

Bituminous Carpet 

Stone-block 

Portland-Cement Concrete 
Brick 

Wood Block 

Sheet Asphalt 



100. Placing the Line. The controlling points of a line are 
certain points at which the position of the road is restricted within 
narrow limits and is not subject to change. These may be points 
where the location is governed by the necessity of providing an out- 
let for the traffic, or points where the position of the line is restricted 
by topographical considerations — such as a summit over which the 
road must pass, or a suitable location for a bridge. 

After the reconnoissance of the locality is completed and the 



* Proc. Amer. Sec. of Civil Engr's, Vol. 42 (1916), p. 1615. 



66 ROAD LOCATION [CHAP. II 

position and elevation of the controlling points are known, the line 
must be marked upon the ground. For example, assume that it is 
desired to run a road from A to D, Fig. 9, page 67, D being a pass 
over the ridge. If the road follows the Hne A B C D, it will have 
the profile shown near the bottom of Fig. 9. The average grade 
from A to 5 is 1 per cent, and from B to C b per cent. If it is de- 
sired to locate a road that shall have a grade no steeper than 5 per 
cent, we may begin at D and locate a Kne having an uniform 5 per 
cent grade. It is best to commence the location from D, since 
usually the slopes nearer the foot of the hills are flatter than those 
at the summit, and consequently there is more choice of position of 
the hne there than at the summit. Frequently in rough countrj^, 
the only controlUng point fixed before beginning the location survey 
is the lowest pass over a ridge or mountain range. 

Beginning at D, a hne may be located either (1) by setting off 
the angle of the gradient on the vertical circle of a transit or on a 
gradienter, and sighting upon a rod which is moved until the hne 
of sight strikes it at the same height from the ground that the instru- 
ment is above grade; or (2) the points for the hne may be found 
by nmning a hne of levels ahead of the transit, and measuring the 
distances by which to reckon the rate of the grade. The hne DEC, 
Fig. 9, has a uniform gradient of 5 per cent. 

If a contour map is at hand, the hne can be located approxi- 
mately by opening a pair of dividers until the distance between the 
points corresponds to 100 feet, setting one point on the place of 
beginning and the other on the next lower contour, which gives a 
line 100 feet long with a grade equal to the distance between con- 
tours — ^in Fig. 9, 5 feet. 

The line D F G has a uniform grade of 5 per cent. From H to A 
the road wiU have considerably less grade than 5 per cent, and can 
have a comparatively wide range of position. 

The average grade from A to D is a little less than 5 per cent, but 
the slopes are so steep between D and C that it is impossible, within 
the hmits of the map, to locate such a hne. If such a gradient is 
located from D toward A, it will necessarily make a number of short 
turns on itself, which, although undesirable, are sometimes un- 
avoidable. These short turns seriously impede traffic, since vehi- 
cles can not easily pass each other on such short curves — particu- 
larly if each is drawn by a long team. Short turns are also danger- 
ous in descending, in case control of the vehicle is lost or the team 
runs away. 



PLACING THE LINE 



67 




101. The line A B C D may be considered as an old road which it 
is proposed to improve by reducing the grades. Substituting the 
hne C E D for CD changes the maximum grade from 10 to 5 per 
cent. 



68 ROAD LOCATION [CHAP. II 

102. In placing the line attention should be given to the nature 
of the soil on alternative lines, since on one side of the valley the 
surface may be clay, upon the opposite gravel; in the bottom of 
the valley the soil is usually alluvial, while higher up it is generally 
better for road purposes. It should be remembered that in almost 
all steep slopes covered with loose material, the debris is either slowly 
moving down the slope or has attained a state of repose so deli- 
cately adjusted that an excavation for a road-bed on the inclined 
surface will again set the mass in motion. Such movements are 
particularly common in loose materials in countries where the frost 
penetrates deeply and the ground becomes very soft when thawing, 
and frequently entail long-continued and serious expense in main- 
tenance. 

If the road is to have a surface of gravel or broken stone, the 
relative proximity of the materials for the original construction as 
well as for repairs should be considered in deciding between possible 
locations. However, it should be remembered that after the road 
is completed, the amount of hauling required to supply materials 
for maintenance must of necessity be small in comparison with the 
ordinary traffic over the road; and hence this consideration should 
not have undue weight. 

Attention should also be given to the disposal of the drainage 
water, and to the question of danger from high water in streams. 
For example, in Fig. 9 it is possible to locate a line on the upper side 
of the map with an imiform grade of 4 per cent, but such a line will 
lie so near the branch entering the main stream at B as to be in 
danger from floods. The matter of crossing streams should receive 
most careful study. Bridges are comparatively expensive to build 
and to maintain. 

It may be cheaper to carry the road across the gully on an em- 
bankment or a trestle than to make a detour around the head of the 
valley. This question can be determined by comparing the greater 
cost of construction of the shorter line with the capitaUzed value 
of the greater cost of operating the longer line. 

In some localities the protection of the road against snow is an 
important matter. Deep cuts almost always catch snow; and for 
this reason it is sometimes better to go around a point by a sup- 
ported grade than to cut through it. In a snow country, roads 
should be located oh slopes facing south and east in preference to 
slopes facing north and west, as the sun has greater power on the 
foi-mer to melt the snow. 



EXAMPLE OF RE-LOCATION 



69 



" Nothing pays like first cost in road building," i. e., money 
expended in intelligent study of the location is the most economical 
expenditure in the construction of a road. 

103. EXAMPLE OF RE-LOCATION. Fig. 10 shows the old and 
the new location of a road. The old location, in the back-ground, 




Fig. 10. — Re-Location of Road. 



had many sharp curves, an undulating profile, and two stream 
crossings; while the new location has easy curves, no needless rise 
and fall, and no stream crossings. 

104. ESTABLISHING THE GRADE LINE. After placing the center 
line, the topography should be taken on each side of the line for 
some distance — ^the distance depending upon the lay of the land; — 
and then a map should be drawn showing the center Hne and ihe con- 
tours. This will serve to show whether the line is placed to the best 
advantage, and whether any changes are desirable. This is especially 
necessary over rough groimd or where the line is on a maximum 
grade. 

The center line for a final location should be carefully run and 
permanently marked, so that it may be re-located if necessary. A 
Une of levels should be run and a profile drawn, upon which the 
grades may be estabhshed and from which the earthwork may be 
estimated (§ 138). 



CHAPTER III 
EARTH ROADS 

106. In 1915 the surface of 87 per cent of the roads of the United 
States was the native earth (Table 12, page 33); and in all prob- 
ability 70 to 80 per cent of these roads will always remain earth 
roads. 

The earth road is the cheapest road in first cost. It is a Hght- 
traffic road, and only when the travel becomes considerable is it 
possible to procure the money with which to improve the surface by 
the use of some foreign material, as gravel or broken stone. For- 
tunately, the best form for the earth road is also the best preparation 
for any improved siu*face. This surface, whatever its nature, is 
only a roof to protect the earth from the effects of weather and travel, 
and any preparation that will enable the native soil when improtected 
to resist these elements will enable it the better to serve as a founda- 
tion for the improved surface! Because of the importance of earth 
roads as a means of transportation and also because of the importance 
of a properly formed and well-drained road-bed for all improved road 
surfaces, earth roads will be considered somewhat fully. 

107. The term earth road will be used as applying to roads whose 
surface consists of the native soil; and, unless otherwise stated, it 
will be understood as meaning a road whose surface is loam or clay. 

Roads on loam and clay will be discussed in this chapter; and 
roads on sand or sand and clay mixed will be considered in the next 
chapter. 

Art. 1. Construction 

108. Width. The width of the right-of-way varies greatly 
but is usually between 40 and 66 feet (§93). With a 66-foot right- 
of-way it is customary to reserve about 6 feet outside of the ditch 
on each side for a foot-way, and to grade the remaining 54 feet. 
With a 40-foot right-of-way it is customary to reserve 6 feet on each 
side for a foot-way, thus leaving 28 feet for ditches and wheelways. 

70 



ART. 1] CONSTRUCTION 71 

For equally good surface drainage, the greater width requires deeper 
ditches and more cost in construction; but permits a wider distribu- 
tion of the travel which is an advantage when the roads are muddy 
or rough. The deep ditches are harder to maintain, and as a rule 
the native soil from the bottom of deep ditches is not so good for road 
building purposes as that nearer the surface. The cost of main- 
taining the road varies with the amount of travel, and is practically 
independent of the width. Therefore the width to be improved 
depends chiefly upon the width of the right-of-way, the character of 
the soil, the climate, and the first cost. In a wet climate, with soil 
easily working into mud, a wide wheelway is desirable; while in a 
dry chmate, or with a soil not readily forming mud, a narrow wheel- 
way is satisfactory. 

109. Width on Curves. For a rule for widening the wheel- 
way on curves, see § 97. This rule hardly appUes to earth roads, 
but it is well to bear it in mind in locating or improving earth roads 
that may ultimately have a hard-surfaced wheelway. 

110. Cross Section. The cross section or transverse contour 
of an earth road is an important matter with reference to the cost of 
construction and maintenance, and depends mainly upon the tools 
or machinery used in construction and maintenance and upon the 
form required for drainage. The subject is discussed fully in 
§ 129-31. 

111. Super-elevation on Curves. For a discussion of the super- 
elevation of the outer edge of the wheelway on curves, see § 90. 

112. Grades. For a general discussion of the effect of both 
maximum and minimum grades upon the use and maintenance of 
a road, see § 79-86. 

The principal problem in reference to grades is the determina- 
tion of the maximum grade permissible. This problem does not admit 
of exact mathematical determination; and therefore recourse must 
be had to experience. For obvious reasons there are not many 
definite data under this head on record. In hilly country short 
grades of 1 in 3 (33%) are occasionally found — particularly in a 
newly settled country, — and grades of 1 in 4 (25%) are somewhat 
common. In a comparatively flat country, grades of 1 in 8 (12i%) 
are not infrequent. 

In improving the celebrated Holyhead road, Telford found in 
old roads many grades of 1 in 6 and 1 in 7. A number of roads 
improved by state aid in New Jersey originally had grades of 14 
per cent. Of course only the roads having the most traffic were 



72 EARTH ROADS [CHAP. Ill 

improved; and probably less frequented roads in each locality have 
much greater grades. 

For mountain roads, where the bulk of the traffic is usually 
down hill, the maximum grade is often 8 per cent and sometimes 
as much as 12 per cent. " Experience in heavy freighting has shown 
that wagons can be satisfactorily controlled in all weather on 
12 per cent grades, but they can not be safely controlled on steeper 
grade." 

113. Drainage. Drainage is the most important matter to 
be considered in the construction of roads, since no road, whether 
earth or stone, can long remain good without it. 

A perfectly drained road will have three systems of drainage, 
each of which must receive special attention if the best results are to 
be obtained. This is true whether the trackway be iron, broken 
stone, gravel, or earth, and it is emphatically true of earth. These 
three systems are underdrainage, side ditches, and surface drainage. 

114. Underdrainage. Any soil in which the standing water in 
the groimd comes at any season of the year within 3 feet of the 
surface will be benefited by drainage; that is, if the soil does not 
have a natural underdrainage, it will be improved for road purposes 
by artificial subsurface drainage. It is the universal observation 
that roads in low places which are thoroughly underdrained dry out 
sooner than undrained roads on high land. Underdrained roads never 
get as bad as do those not so drained. Underdrainage without 
grading is better than grading without drainage; and, in general, 
it may be said that where the soil does not have natural under- 
drainage, there is no way in which road taxes can be spent to better 
advantage than in subsurface drainage. Underdrainage is the very 
best preparation for a gravel or stone road. Gravel or broken 
stone placed upon an undrained foundation is almost sure to sink 
(perhaps slowly, but none the less surely), whatever its thickness; 
whereas a thinner layer upon a drained road-bed will give much 
better service. 

115. The Object. The opinion is quite general that the sole 
object of underdrainage is to remove the surface water, but this is 
only a small part of the advantages of the underdrainage of roads. 
There are three distinct objects to be gained by the artificial under- 
drainage of a wagon road. 

1. The most important object is to lower the water level in the 
soil. The action of the sun and the wind will finally dry the surface 
of the road; but if the foundation is wet, it will be soft and spongy. 



ART. 1] CONSTRUCTION 73 

the wheels will wear ruts, and the horses' feet will make depressions 
between the ruts. The first shower will fill these depressions with 
water, and the road will soon be a mass of mud. A good road can 
not be maintained without a good foundation, and an undrained soil 
is a poor foundation, while a dry subsoil can support almost any 
load. 

2. A second object of underdrainage is to dry the ground quickly 
after a freeze. When the frost comes out of the ground in spring, 
the thawing is quite as much from the bottom as from the top. If 
the land is underdrained, the water when released by thawing from 
below will be immediately carried away. This is particularly im- 
portant in road drainage, since the foundation will then remain soHd 
and the road itself will not be cut up. Undei'drainage will usually 
prevent the " bottom dropping out " when the frost goes out of the 
ground. " 

3. A third, and sometimes a very important, object of subdrainage 
is to remove what may be called the underflow. In some place©- 
where the ground is comparatively dry when it freezes in the fall, it 
will be very wet in the spring when the frost comes out — surpris- 
ingly so considering the dryness before freezing. The explanation 
is that after the ground freezes, water rises slowly in the soil by 
the hydrostatic pressure of water in higher places; and if it is not 
drawn off by underdrainage it saturates the subsoil and rises a. 
the frost goes out, so that the ground which was comparatively dry 
when it froze is practically saturated when it thaws. 

118. The underdrainage of a road not only removes the water, 
but prevents, or greatly reduces, the destructive effect of frost. 
The injurious effect of frost is caused entirely by the presence of 
water; and the more water there is in the road-bed the greater the 
injury to the road. The water expands on freezing, the surface of 
the road is upheaved, and the soil is made porous; when thawing 
takes place, the ground is left honeycombed and spongy, ready to 
settle and sink, and under traffic the road " breaks up." If the 
road is kept dry, it will not break up. Underdrainage can not pre- 
vent the surface of the road from becoming saturated with water 
during a rain, but it is the best means of removing surplus water, 
thus allowing the surface to dry and preventing the subsequent 
heaving by frost. 

That frost is harmless where there is no moisture, is shown on a 
large scale in the semi-arid regions west of the Mississippi river. 
The ground there is normally so dry that during the winter, when 



74 EARTH ROADS [CHAP. Ill 

it is frozen, cracks half an inch or more wide form, owing to the dry- 
ing and consequent contraction of the soil, which shows that there 
is no expansion by the freezing of water in the soil; and therefore 
in this region there is no heaving or disturbance by frost. 

117. The Tile. The best and cheapest method of securing under- 
drainage is to lay a Hne of farm tile 3 or 4 feet deep on one or both 
sides of the roadway. The ordinary farm tile is entirely satis- 
factory for road drainage. It should be uniformly burned, straight, 
round in cross section, smooth inside, and have the ends cut off 
square. Tile may be had from 3 to 30 inches in diameter. The 
smaller sizes are usually a little over a foot long, — ^the excess length 
being designed to compensate for breakage; and the larger sizes 
are nominally 2 or 2J feet long, but usually a Httle longer. The 
cost of tile free on board at the factory is usually about as in Table 
17, page 75. Y's for connections can be had at most factories, but 
they cost four or five times as much as an ordinary tile. With 
patience and a Httle experience ordinary tile can be cut to make 
fairly good connections. 

Before the introduction of tile for agricultural drainage, it was 
customary to secure underdrainage by digging a trench and deposit- 
ing in the bottom of it logs or bundles of brush, or a layer of stone; 
or a channel for the water was formed by setting a line of stones 
on each side of the trench and joining the two with a third line 
resting on these two. Apparently it is still the practice in some 
localities to use such substitutes for ordinary drain tile. Tiles are 
better, since they are more easily laid and are less Hable to get 
clogged. Tiles are cheaper in first cost, even when shipped consid- 
erable distances by rail, than any substitute; and the drains are 
much more durable. 

Tiles are laid simply with their ends in contact, care being taken 
to turn them until the ends fit reasonably close. In some localities 
there is apparently fear that the tile will become stopped by fine 
particles of soil entering at the joints, and consequently it is specified 
that the joints shall be covered with tarred paper or something of the 
sort; but in the Mississippi Valley, where immense quantities of tile 
have been laid, no such difficulty has been encountered. With a 
very slight fall or even no fall at all, tiles will keep clean, if a free 
outlet is provided, and they are not obstructed by roots of trees — 
particularly willow. 

In some locahties it is apparently customary to use collars 
around the ends of the tile to keep them in line. If the bottom of 



ART. 1] 



CONSTRUCTION 



75 



the trench is made but little wider than the diameter of the tile, or 
if a groove is scooped out in the bottom of the trench to fit the tile, 
no difficulty need be apprehended from this source. 

TABLE 17 
Cost and Weight of Drain Tile 



Inside 


Price per 1000 Ft. 


Weight 


Number of Feet 


Diameter. 


f.o.b. Factory. 


per foot. 


in a Car Load. 


3 inches 


$10.00 


5 1b. 


7 000 


4 " 


15.00 


7 " 


6 500 


5 " 


20.00 


9 " 


5 000 


6 " 


27.00 


12 " 


4 000 


7 '' 


35.00 


14 " 


3 000 


8 " 


45.00 


18 " 


2 500 


9 " 


55.00 


21 '' 


1800 


10 '' 


65.00 


25 " 


1600 


12 '' 


90.00 


33 " 


1000 


14 " 


120.00 


43 " 


800 


16 '' 


150.00 


50 " 


600 


18 " 


240.00 


70 " 


400 


20 " 


300.00 


83 " 


330 


24 " 


360.00 


112 '' 


300 



118. The Fall There is no danger of the grade of the tile being 
too great, and the only problem is to secure sufficient fall. A num- 
ber of authorities on farm drainage and also several engineering 
manuals assert that a fall of 2j or 3 inches per 100 feet is the lowest 
hmit that should be attempted under the most favorable conditions; 
but practical experience has abundantly proved that a much smaller 
fall will give good drainage. In central IlUnois and northern 
Indiana there are many fines of tile having falls of only | to J of an 
inch per 100 feet which are giving satisfactory drainage; and not 
infrequently ordinary tile laid absolutely level directly upon the 
earth in the bottom of the trench, without coUars or other covering 
■ over the joints, has given fairly good drainage without trouble from 
the deposit of sediment. Of course, extremely flat grades are less 
desirable than steeper ones, since larger tile must be used, and 
greater care must be exercised in laying them, and since there is 
more risk of the drain's becoming obstructed; but these extremely 
flat grades are sometimes all that can be obtained, and even such 
drains abundantly justify the expense of their construction. 

If possible at reasonable expense, the grade should be at least 
2 inches per 100 feet; and unless absolutely necessary should never 



76 EARTH ROADS [CHAP. Ill 

be less than | inch per 100 feet. On level or nearly level ground 
the fall may be increased by laying the tile at the upper end shallower 
than at the lower. 

119. Size of Tile. The following formula has frequently been 
employed to determine the size of tile: 



^■^^\{d^ (1) 



in which A is the number of acres for which a tile having a diameter 
of d inches and a fall of / feet in a length of I feet will remove 1 
inch in depth of water in 24 hours. 

Equation (1) is based on the formula ordinarily employed for 
the flow of water through smooth cast iron pipe, and is only roughly 
apphcable to tile. It probably gives too great a capacity lOr tile. 
However, all the factors of the problem are too uncertain to justify 
an attempt at mathematical accuracy. For example, we can not 
know with any certainty the maximum rate of rainfall, the duration 
of the maximum rate, the permeability of the soil, the amount of 
water retained by the soil, the effect of surface water flowing onto the 
road from higher ground, the area to be drained, etc. The above 
formula is useful only in a locality where there is no local experience 
with tile ; and its chief value consists in showing the relation between 
capacity and grade, and the effect of a variation in the diameter of 
the tile. 

The object of underdraining a road is to prevent the plane 
of saturation from rising so near the surface as to soften the 
foundation of the road even during a wet time, and therefore the 
provision for underdrainage should be Hberal; but what will be 
adequate in any particular case depends upon the amount of traffic, 
the local topographic conditions, the character of the soil, etc. The 
best practice in agricultural drainage provides for the removal of 
0.5 to 1 inch of water per day; but since the side ditches will assist 
in removing rain water from the road, it is probable that a provision 
for the removal of half an inch per day is sufficient for the under- 
drainage of a road. If there is an underflow of water from higher 
ground, or if the ground is " springy," then the ordinary provisions 
for underdrainage should be increased. 

120. It is not wise to lay a smaller tile than a 4-inch one, and 
probably not smaller than a 5-inch. Tile can not be laid in exact 
line, and any tilting up of one end reduces the cross section. Again, 



ART. 1] CONSTRUCTION 77 

if there is a sag in the Une equal to the inside diameter, the tile will 
shortly become entirely stopped by the deposit of silt in the depres- 
sion. 

It is sometimes wiser to lay a larger tile than to increase the fall. 
Ordinarily, the deeper the tile the better the drainage, although SJ 
or 4 feet deep is usually sufficient. 

121. Laying the Tile. It is unwise to enter upon any detailed 
discussion of the art of laying tile. The individual tiles should 
be laid in Une both vertically and horizontally, with as small joints 
at the end as practicable. Care should also be taken that the tile 
is laid to a true grade, particularly if the fall is small, for if there is 
a sag it will become filled with sediment, or if there is a crest silt 
will be deposited just above it. The drain should have a free and 
adequate outlet. The end of the fine of tile should be protected 
by masonry, by plank nailed to posts, or by replacing three or four 
tiles at the lower end by an iron pipe or a wooden box. 

122. Cost of Laying Tile. On the basis of 15 cents an hour for 
common labor, the prevailing cost of laying tile in loam with clay 
subsoil is about as follows: for 8-inch tile or less, 10 cents per rod 
for each foot of depth; for 9-inch, 11 cents; for 12-inch, 14 cents; 
for 15-inch, 17 cents; and for 16-inch, 18 cents. To aid in remem- 
bering the above data, notice that the price is 10 cents per rod 
per foot of depth for 8-inch tile or less, with an increase of 1 cent 
for each additional inch of diameter. 

The cost of a mile of 5-inch tile drain is usually from $200 to 
$250, exclusive of freight on the tile. If there is any considerable 
amount of tifing, the above prices for the smaller tile can be reduced 
10 to 20 per cent; and often there is enough discount on the prices 
given in Table 7, page 75, to cover the railroad freight-charges. 
A tile drain is a permanent improvement with no expense for main- 
tenance, the benefit being immediate and certain; and therefore it 
is doubtful if money can be spent on earth roads to better advan- 
tage than in laying tile. 

123. One vs. Two Lines. Usually a line of tile 2j to 3 feet deep 
under the ditch at one side of the road will give sufficient drainage. 
In case of doubt as to whether one or two fines of tile are needed, 
put in one and watch the results. If both sides of the road are 
equally good, another tile drain is not needed. In making these 
observations care should be taken not to overlook any of the con- 
tingent factors, as, for example, the difference in the effect of the sun 
upon the south and the north sides of the road, the effect of shade 



78 EARTH ROADS [cHAP. Ill 

or of seepage water, the transverse slopes of the surface of the 
road, etc. 

124. Location of Tile. Some writers on roads recommend a 
Hne of tile under the middle of the traveled portion. With the 
same depth of digging, a tile under the side ditch is more effective 
than one under the center of the road. Further, if the tile is under 
the center, there is liability of the settling of the soil in the trench, 
which will make a depression and probably a mud hole; and if the 
tile becomes stopped, it is expensive to dig it up, and the doing so 
interferes with traffic. Finally, if the road is ever graveled or 
macadamized, the disadvantage of having the tile drain under the 
center of the road is materially increased. 

Some writers advocate the use of a line of tile near the surface, 
on each side of the trackway. The object of placing the tile in this 
position is to secure a rapid drainage of the surface; but very Httle, 
if any, water from the surface will ever reach a tile so placed, since 
the road surface when wet is puddled by the traffic, which pre- 
vents the water's percolating through the soil. It is certain that 
in clay or loam the drainage thus obtained is of no practical value. 
Many farmers have tried to drain their barn-yards by laying tile 
near the surface, but always without appreciable effect. The 
deeper the tile the better the drainage. 

The rapid surface drainage sought by putting a tile or its equiva- 
lent near the surface, can best be secured by giving the surface of 
the road a proper crown and keeping it free from ruts and holes 
(§ 205.) 

While a Hne of tile on one side of the road is usually sufficient, 
there is often a great difference as to the side on which it should be 
laid. If one side of the road is higher than the other, the tile should 
be on the high side to intercept the ground water flowing down the 
slope under the surface. Sometimes a piece of road is wet because 
of a spring in the vicinity, or perhaps the road is muddy because 
of a stratum which brings the water to the road from higher ground ; 
in either case, the source of supply should be tapped with a line 
of tile instead of trying to improve the road by piling up earth. 

125. Side Ditches. The side ditches are to receive the water 
from the surface of the traveled way, and should carry it rapidly and 
entirely away from the roadside. They are useful, also, to inter- 
cept and carry off water that would otherwise flow from the side 
hills upon the road. Ordinarily they need not be deep; but, if 
possible, should have a broad, flaring side toward the traveled way. 



ART. 1] CONSTRUCTION 79 

to prevent accident if a vehicle should be crowded off the side of 
the roadway. The outside bank should be flat enough to prevent 
caving. 

If the road is tiled as above recommended, the side ditch need 
not be very large; but it should be of such a form as to permit its 
construction with the road machine or scraping grader (§ 155) or 
with a drag scraper (§ 150), instead of by hand. On comparatively 
level ground, the proper form of side ditch is readily and cheaply 
made with the usual road machine. Fig. 11, page 82, shows a shal- 
low ditch of the proper form; and Fig. 12 shows a deeper one of the 
same general form. If a larger ditch is needed, it should be of such 
a form as to be made chiefly with the drag-scoop scraper. 

A deep narrow ditch is expensive to maintain, since it is easily 
obstructed by caving banks, by weeds, and by floating trash. For- 
tunately the shallow ditch is easy and cheap to construct and also 
to maintain. If it is necessary to carry water along the side of the 
road through a rise in the ground, it is much better to lay a hne 
of tile and nearly fill the ditch than to attempt to maintain a narrow 
deep ditch. A tile is much more effective per unit of cross section 
than most open ditches. 

126. The side ditch should have a uniform grade and a free out- 
let into some stream, so as to carry the water entirely away from 
the road. No good road can be obtained with side ditches that 
hold the water until it evaporates. For this reason much ostensible 
road work is a positive damage. Piling up the earth in the middle 
of the road is perhaps in itself well enough, but leaving undrained 
holes at the side probably more than counterbalances the benefits 
of the embankment. A road between long artificial ponds is always 
inferior and is often impassable. It is cheaper and better to make 
a lower embankment, and to drain thoroughly the holes at the side 
of the road. PubHc funds often can be more widely used in making 
ditches in adjoining private lands than in making ponds at the 
roadside in an attempt to improve the road by raising the surface. 
It is cheaper and better to aUow the water to run away from the road 
than to try to lift the road out of the water. 

When the road is in an excavation, great care should be taken 
that a ditch is provided on each side to carry away the water so that 
it shall not run down the middle of the road. Every road should 
have side ditches, even one that runs straight down the side of a 
hill. Indeed, although it often has none, the steepest road needs the 
side ditch most. Frequently the water runs down the middle of 



80 EARTH ROADS [CHAP. Ill 

the road on a side hill and wears it into gullies, which are a discom- 
fort, and often dangerous, in both wet weather and dry. 

In a slightly rolling country, the side ditch frequently has no 
outlet, and the water is allowed to accumulate at the foot of the 
slope and there remain until it is absorbed by the ground or seeps 
into the tile drain. The water seeps away very slowly because the 
fine silt carried down by the water fills up the pores of the native 
soil and renders it nearly impervious. The difficulty could be 
remedied by providing an inlet from the open ditch to the tile. This 
may be a well, walled with plank or masonry without mortar (except 
near the top; and having a grating in the side or top through which 
the water may pass. The well should be large enough to allow a 
man to enter it to clean it, and should extend a foot or more below 
the bottom of the tile. Earth roads in villages and towns are usually 
better provided with such inlets than country roads, but both could 
be materially improved at comparatively small expense by pro- 
viding inlets from the side ditch into the tile. 

127. If it can be prevented, no attempt should be made to carry 
water long distances in side ditches; for large bodies of water are 
hard to handle, and are liable to become very destructive. Side 
ditches should discharge frequently into the natural watercourses, 
though to compass this, it may in some cases be necessary to carry 
the water from the high side to the low side of the road. This is 
sometimes done by digging a gutter or by building a dam diagonally 
across the road, but both are ver}^ objectionable. A better way 
is to lay a tile or put in a culvert (Fig. 53, page 198), the amoimt 
of water determining which shall be done. 

It is sometimes necessary to carry water a considerable distance 
in the side ditches, as, for eaxmple, when the road is in excavation. 
This requires deep ditches, which are undesirable and dangerous; 
and if the grade is considerable, the ditches wash rapidly. In such 
cases, it is wise to lay a fine of tile under the side ditch, and at 
intervals turn the water from the surface ditch into the tile drain. 
This can be accomplished readily by inserting in the line of porous 
tile a Y section of vitrified pipe, with the short arm opening up hill. 
Of course, the short arm, i. e., the vertical arm, need not be as large 
as the body. If necessary, two or three lengths of porous tile may 
be added at the upper end of the Y to make connections with the 
bottom of the open ditch. Earth, sods, or stones, can be piled 
around the upper end of the tile to make a dam and to hold the tile 
in place. 



ART. 1] CONSTRUCTION 81 

Some road engineers lay a line of tile under the side ditch, and 
fill the trench with broken stone, thus making the tile carry both 
the surface water and the underdrainage. This practice probably 
affords better surface drainage, but it costs more than to allow the 
surface water to flow away in the side ditches. This construction 
is sometimes defended on the ground that the broken stone prevents 
the wheels from striking the tile when vehicles in passing are forced 
into the ditches. This danger does not seem very great, and would 
not occur at all if the tile were laid at the proper depth; but this is 
sometimes impossible owing to a hard substratum. 

128. As a rule side ditches will not have too much fall; but 
sometimes a ditch straight down a hill will have so much as to wash 
rapidly, in which case it is an advantage to put in an obstruction of 
stone or brush. In extreme cases the bottom of the ditch is paved 
with stones. 

129. Surface Drainage. The drainage of the surface of a road 
is very important, and is provided for by crowning the surface 
and keeping it smooth. It should be remembered that water upon 
the surface of the road can not be carried away by the underdrains, 
since the water can reach them only after it has penetrated and 
softened the road surface. The slope from the center to the side 
should be enough to carry the water freely and quickly to the side 
ditch; and if the surface is kept free from ruts and holes, less crown 
wiU suffice than if no attention is given to keeping the surface smooth. 
If there is not enough crown, the water can not easily reach the 
side ditches; and hence the road soon becomes watersoaked. 

On the other hand, the crown may be too great. If the side 
slopes are so steep that traffic keeps continually in the middle, the 
road will be worn hollow and retain the water instead of shedding it 
promptly to the side ditches. If the crown is too great, it is difficult 
for vehicles to turn out in passing each other. Again, if the earth 
is piled too high in the middle, the side slopes will be washed into 
the side ditches, which not only damages the road but also fills up 
the ditches. Further, if the side slopes are steep, the top of the 
wheel will be further from the center of the road than the bottom; 
and the mud picked up by the bottom of the wheel will be carried to 
the top of the wheel and then dropped farther from the center of the 
road than it was before, each passing vehicle moving the earth 
from the center toward the side of the road. Finally with the 
ordinary method of caring for earth roads, more water stands on a 
very convex road than on a flatter one. 



S2 i:arth roads [chap, hi 

The slope from the center to the side should be at least half an 
inch to a foot, or 1 foot in 24 feet; and it should not be more than 1 
inch to a foot, or 1 foot in 12 feet. If the surface is well cared for, 
the former is better than the latter; but in no case is it wise to 
exceed the latter slope. 

Some claim that theoretically the cross section of the surface 
should be the arc of a circle, and others that it should consist of 
two planes meeting at the center and having their junction rounded 
off with a short curve. Great refinement in this matter is neither 
possible nor important. Two examples of a properly crowned 
road are shown in Figs. 11 and 12. The crown can be easily and 
cheaply constructed with the scraping grader (§155). 



■6ff. ^fQin.\* 7ft 6in — ^ fdff: 

J2in. 



n»//7.h*— 

Fig. 11. — Road Surface an Arc. Shallow Side Ditch. 

The drainage of the surface of a road is chiefly a matter of main- 
tenance (see Art. 2 of this chapter); and one of the most common 
defects of maintenance is the failure to fill ruts and keep the surface 
smooth so that the water will be promptly discharged into the side 
ditches. A comparatively shallow rut will nulhfy the effect of any 




OS/n. Ti/e 

Fig. 12. — Road Surface an Arc. Deep Side Ditch. 

reasonable amount of crown. Seldom is a mile of road seen which 
does not have a number of ruts and saucer-hke depressions which 
catch and hold the water. On undulating roads, ruts and holes are 
naturally drained; and this is the reason why undulating roads are 
better than perfectly flat ones (see Minimum Grade, §86). 

Fig. 13 shows a form of cross section sometimes adopted for 
earth roads in villages and towns. The gutter usually is made next 
to the sidewalk, which is objectionable, since horses must stand 
in the mud and water when hitched in front of the abutting prop- 
erty. The form shown in Fig. 12 is free from this objection, A nar- 
row berm is left between the sidewalk and the edge of the slope to 
prevent crowding the gutter too close to the shade trees, which are 



\ 



ART. 1] CONSTRUCTION ^KBKP 83 

usually planted just outside of the sidewalk. The gutter shown in 
Fig. 12 decreases the available wheel way, and consequently in some 
localities would be undesirable. This cross section also can be made 
and maintained with the ordinary scraping grader. 



k — a/"/ ^ — dff 



Wa/k 



.-^ iJft 



Fig. 13. — Cross Secttion op Village Street. 

130. The crown should be greater on steep grades than on the 
more level portions, since on the grade the line of steepest descent is 
not perpendicular to the length of the road, and consequently the 
water in getting from the center of the road to the side ditches travels 
obliquely down the road. If the water once commences to run 
down the center of the roadway on a steep grade, the wheel tracks 
are quickly deepened, and the road becomes rough and even danger- 
ous. Under these circumstances, it is necessary to construct catch- 
waters (" water-breaks," '' hummocks," or " thank-you-marms ") 
at intervals to catch the water which runs longitudinally down the 
road, and to convey it to the side ditches. These catch-waters may 
be either broad shallow ditches or low flat-ridges constructed across 
the road; and they may slope toward one or both side ditches. In 
the former case, they should cross the road diagonally in a straight 
hne; and in the latter case, in plan they should be a broad angle 
with the apex at the center of the road and pointing up hill. There 
is little or no difference between the merits of the ditch and the ridge, 
unless the bottom of the former is paved with gravel, broken stone, 
or cobbles. The ridges are more common, but usually are so narrow 
and so high as to form a serious obstruction to travel, a fact which 
is especially objectionable since the introduction of the automobile. 
However, neither the ditches nor the ridges should be used except 
on steep grades where really necessary, since either form is at best 
an obstruction to travel. The angle that the catch-waters shall 
have with the axis of the road should be governed by the steepness 
of the grade — the steeper the grade the more nearly should the 
catch- waters run down the road. They should have a considerable 
breadth so that wheels may easily ascend them and horses will not 
stumble over them. 

Catch-waters should be constructed also in a depression where 
an ascending and a descending grade meet, in order that they may 
collect the water that runs down the traveled way and convey it 



84 EARTH ROADS [CHAP. Ill 

into the side ditches. These catch-waters should run square across 
the road, and should be quite shallow ditches, the bottom of which 
should be hardened with gravel, broken stone, or cobbles. 

131. Some writers recommend that the surface of a road on the 
face of a hillside should consist of a single slope inclining inwards 
(see Fig. 14). This form of surface is advisable on sharp curves, but 




Fig. 14. — Improper Cross Section op Road on Side Hill. 

is of doubtful propriety elsewhere. The only advantage of this 
form is that the water from the road is prevented from flowing down 
the outer face of the embankment; but the amount of rain water 
falHng upon one half of the road can not have a very serious effect 
upon the side of the embankment. With a roadway raised in the 
center and the water draining off to either side, the drainage will be 
more effectual and speedy than if the drainage of the outer half 
must pass over the inner half. If the surface is formed of one plane, 
as in Fig. 14, the lower half of it will receive the greater share of the 
travel as the tendency is to keep away from the edge; and as this 
part of the surface will bo more poorly drained, it is nearly certain 
to wear hollow. This will interfere with the surface drainage; and 
consequently a road with this section will require excessive attention 
to keep it in good condition. Figs. 53 and 54, page 198, show two 
forms of Swiss hillside roads having the center higher than either 
side. 

Whatever the form of the road surface, if the hillside is steep 
there should be a catch-water above the road to prevent the water 
from the hillside above flowing down on the road. Fig. 14 shows 
such a catch-water. It should be, say, 6 feet back from the 
excavation, and should have a width and depth according to the 
amount of water to be intercepted. 

132. Excavation and Embankment. Side Slopes. The 
angle of the slopes of the cuts and fills is designated by the ratio of 
the horizontal to the vertical distance. Thus, if the face of the fill 



■ 



ART. 1] CONSTRUCTION 85 

has an inclination of Ij feet horizontal to 1 foot vertical, the slope is 
designated as 1| to 1. 

The slope of the excavations varies with the nature of the soil, 
being for economy as steep as the tenacity of the soil will permit. 
Solid rock may be cut with a slope of J to 1. Common earth will 
stand 1 to 1, or 1 J to 1 — the latter being safer and more usual. Gravel 
requires Ij to 1. Some clays will stand 1 to 1, while some require 
a much flatter slope — in extrene cases 6 to 1. Fine sand requires 
a slope of 2 to 1, or 3 to 1. 

The slope of embankment has less range than that of excava- 
tions, since there is less variety in the nature and the condition of 
the materials, and is usually 1| to 1. 

133. In both railroad and wagon-road work, it is customary to 
establish all earthwork slopes as planes intersecting each other in 
right hues. The original form is never maintained, since it is not a 
form of equilibrium and stability. Storm water soon washes away 
the angle formed by the intersection of the two plane surfaces at the 
top of the embankment, and the water flowing down the slope soon 
rounds out the angle at the foot. Such construction violates one of 
the fundamental principles of stabihty, and it is a needless expense to 
build laboriously a form of construction which nature will inevitably 
destroy. 

The transverse contours of the embankment and excavation 
shown in Figs. 15 and 16 are designed to meet the above objections 



#1 



-Cross Section for Embankment, 



to the ordinary forms of construction. These sections are de- 
signed in accordance with the forms of railroad excavations and 




I / 07%- OTile \\ 

Fig. 16. — Cross Section for Excavation. 

embankments recommended by D. J. Whittemore, the distinguished 
chief engineer of the Chicago, Milwaukee and St. Paul Railroad, 



EARTH ROADS [CHAP. Ill 



whose forms have met with the unanimous approval of leading 
engineers. , 

It is customary in railroad construction to make the top of the 
earth embankment wider than the base of the gravel or broken- 
stone ballast, which gives a berm between the base of the ballast 
and the outer edge of the earth embankment. This berm has been 
omitted in Figs. 15 and 16, since with an earth surface there is 
nothing corresponding to the ballast. 

134. If the natural slope above the cut is long or steep, a catch- 
water drain should be constructed along the upper edge of the exca- 
vation slope to prevent the surface water from above washing 
down over the face of the cut; but the catch-water should be weU 
back from the edge of the excavation, to prevent the water in the 
drain from softening the upper angle of the slope (Fig. 14, page 84). 

The slopes of both excavations and embankments should be 
sowed with grass seed. Sometimes the material of the embank- 
ment is such that grass seed will not grow, in which case it may be 
necessary to lay sod; but of course this is very expensive. The 
I Dots of the grass will hold the earth from sUpping, and prevent 
the face of the slope from being gullied out and washed down. 

135. There is a tendency for workmen in order to decrease the 
amount of labor required to leave the side slopes of embankments 
hollow and those of excavations rounding. When inspecting the 
work, this tendency should be borne in mind. 

136. Setting Siope Stakes. For instructions as to methods of 
staking out the ground preparatory to beginning the work of exca- 
vating and embanking, see any of the standard volumes on railroad 
engineering. 

137. Computing Earthwork. For the methods employed in 
computing the contents of excavations and embankments, see any 
of the various treatises on that subject; or for a briefer presentation 
of the subject, see books on surveying or railroad engineering. 

138. Balancing Cuts and Fills. Other things being equal, the 
most economical position of the grade Hne is that which makes the 
amount of cuts and fills equal to each other. If the cuts are the 
greater, the earth therefrom must be wasted, i. e., deposited in spoil 
banks; and if the fills are the greater, the difference must be ob- 
tained from borrow pits, — both of which operations involve addi- 
tional expense for labor and land. Sometimes it is more economical 
to make an embankment from near-by borrow pits than to bring 
the necessary material from a far-distant cut; or, vice versa, it is 



ART. 1] CONSTRUCTION 87 

sometimes more economical to waste the material from a cut than 
to send it to a remote fill. The most economical use of the material 
depends upon the machinery used in moving the earth, the char- 
acter of the earth in both cuts and fills, the road over which the 
earth must be transported, the cost of haul, the price of land, the 
liabihty of cuts being filled with snow, etc.; and the matter must 
be decided by the engineer to the best of his judgment in each 
particular case. 

When the road lies along the side of a hill, one side of the road is 
usually in cut and the other in fill; and it is customary so to place 
the center fine that these two parts are at least nearly equal. How- 
ever, where the side slopes are steep, it is better to make the road 
mostly in cuts on account of the difficulty of forming stable fills on 
steep slopes. 

139. In railroad work it is the custom to balance cuts and fills 
on the longitudinal profile of the road, but in wagon-road work the 
fills as shown by the profile of the center line should be slightly in 
excess, to provide a place for the earth taken from the side ditches. 
On account of the expense, wagon roads follow the surface more 
nearly than railroads; and consequently the earth from the ditches 
is proportionally more in wagon-road construction than in railroad 
construction. 

140. Shrinkage of Earthwork. With the ordinary soil, the act of 
excavation so breaks it up that it occupies more space after excava- 
tion than before; but when the material has been placed in an 
embankment it will usually occupy less space than in its original posi- 
tion. The expansion due to excavation is usually 8 to 12 per cent 
of the volume, and in extreme cases m.ay be 40 per cent; but in 
placing the material in the embankment, it is compacted by the 
weight of the embankment itself, by the pounding of the hoofs and 
by the action of the wheels, until usually the final volume is less 
than the original. 

At first thought it seems strange that earth should occupy less 
space when placed in an embankment than when in its original 
position, seeing that it is not so hard and firm, and that it will 
usually settle still farther after the embankment is completed. 
The following facts account for this phenomenon: 1. The continued 
action of frost has made the soil in its natural position more or less 
porous. 2. Earths which have been lying in situ for centuries 
become more or less porous through the slow solution of their soluble 
constituents by percolating water. 3. The surface soil is rendered 



B8 EARTH ROADS [cHAl>. HI 

more or less porous by the penetration of vegetable roots which 
subsequently decay. 4. There is ordinarily more or less soil lost 
or wasted in transporting it from the excavation to the embank- 
ment. 

The amount of shrinkage depends chiefly upon the character of 
the material and the means by which it is put into the embankment, 
and somewhat upon the moisture of the soil, the rainfall conditions 
while the work is in progress and soon afterwards, and the depth to 
which frost usually penetrates. If the soil is moist when placed in 
the bank, it will become more compact than if it is dry. Rain 
greatly affects the shrinkage, and embankments put up during a 
rainy season will be more compact than those built during a dry 
time. Soil from above the usual frost line is more porous than that 
not subject to the heaving effect of alternating freezing and thawing, 
and consequently shrinks more when put into an embankment. 

The natural shrinkage of the ordinary soils is in the following 
order: (1) sand and sandy gravel least, (2) clay and clayey soil 
intermediate, and (3) loams most. The shrinkage according to 
the method of handling is in the following order, beginning with 
the least: (1) drag scrapers, (2) wheel scrapers, (3) wagons, (4) cars, 
(5) wheelbarrows. The usual allowance for shrinkage for drag- 
scraper work is as follows: gravel 8 per cent, gravel and sand 9 
per cent, clay and clayey earth 10 per cent, loam and Hght sandy 
earth 12 per cent, loose vegetable surface-soil 15 per cent. The 
above results are for ordinary earth, and do not apply to such 
unusual materials as " buckshot," gumbo, very fibrous soil,, etc., 
which have a much greater shrinkage. Solid rock will expand 40 
to 50 per cent. 

The shrinkage of earth should be considered in locating the grade 
lines to balance the cuts and fills. 

141. Settlement of Embankments. The shrinkage of earth- 
work referred to above takes place chiefly during construction, but 
the continued action of the weight of the embankment and the 
effect of rain and traffic will usually cause a comparatively small 
settlement after completion. Sand or gravel embankments built 
with wheel scrapers will usually settle 1 to 2 per cent after comple- 
tion, and clay or loam embankments about 2 to 3 per cent. With 
drag scrapers the settlement will usually be a Httle less than the 
above; and with dump carts or wagons, a httle more. With wheel- 
barrows the settlement is usually about 10 per cent, but may be as 
much as 25 per cent, depending upon the moisture in the soil, the 



1 



AET. 1] CONSTRUCTION 89 

rain during construction, and the length of time under construc- 
tion. 

The settlement of the embankment after completion should be 
taken into account when determining whether the bank has been 
raised to the proper height. The embankment should be built to 
such a height that after it has ceased to settle it will be at grade. 
The length of time required for this settlement depends upon the 
weather conditions. The proper adjustment of the height of the 
embankments to compensate for future settlement is an important 
matter with broken-stone roads and with pavements. 

142. The above remarks about settlement do not apply to em- 
bankments built with the elevating grader (§ 161). The settle- 
ment of earth roads put up by these machines is of no importance, 
and depends upon the amount of rolhng they receive. 

143. Rolling the Embankment. Many writers on roads rec- 
ommend the rolhng of all new earth embankments. In view of 
the usual settlement of banks built with drag or wheel scrapers, it 
does not appear that rolhng with a farm roller would be very effect- 
ive, and a heavier roller is seldom available. Simply rolhng the 
top of the finished bank is not worth much, since the effect of the 
roller does not reach very deep; and, besides, no roller will compact 
loose earth so that wheels and hoofs will not make depressions in 
it.* Further, it is not practicable to roll the bank during the 
progress of construction, except when the scraping and elevating 
graders are used. Finally, those who travel the road most are gen- 
erally the ones who pay for the construction, and almost univer- 
sally they prefer to compact the earth by traffic. 

It is customary to roll the foundation of pavements, but the 
chief object of so doing is to discover soft places rather than to con- 
sohdate the surface; and, besides, the foundation of a pavement is 
protected from rain and the action of wheels, and therefore the 
effect of the rolhng is permanent, while with an earth road it is not. 

144. Over-haul. When earthwork is done by contract, the bid 
includes the cost of removing excavated material and depositing 
it in embankments, provided the necessary length of haul does not 
exceed a specified limit. When the material must be carried beyond 
this hmit the extra distance is paid for at stipulated price per cubic 
yard per 100. feet of haul. This extra distance is known by the 
name of '' over-haul " or simply '' haul." For an explanation 

* The heaviest steam rollers give a pressurfe of about 600 pounds per linear inch, while 
wagons frequently give twice, and occasionally three times, as much. 



90 EARTH ROADS [CHAP. Ill 

of the method of computing '' haul," see treatises on earthwork or 
books on railroad surveying. 

The specified limit, i. e., the distance of free haul, depends upon 
the conditions. It is sometimes made as low as 100 feet, and is 
sometimes 2,000 feet — the latter usually only in street work. In 
railroad work 500 feet is a common Hmit. 

145. Frequently all allowances for over-haul are disregarded. 
The profiles, estimates of quantities, and the required disposal of 
material are shown to bidding contractors; and they must then 
make their own allowances, and bid accordingly. This method has 
the advantage of avoiding possible disputes as to the amount of the 
over-haul allowance, and on this account is adopted by some railroads. 

146. Stability of Embankments. The principles to be observed 
in the formation of an embankment depend somewhat upon the 
machinery employed in doing the work, but a few general considera- 
tions are not out of place here. 

Specifications usually require that '' all matter of vegetable 
nature must be carefully excluded from the embankment." It is 
impracticable to do this v/hen the road passes through grass land — 
particularly if the grade is built with a scraping grader (§ 155). 
It is desirable to remove brush, tall grass, and high weeds from the 
space to be occupied by the embankment and the borrow pit; but 
small twigs, leaves, and sod are no material detriment, and their 
removal is a needless expense — except at the point where the road 
passes from cut to fill. It is essential that all vegetable matter 
and loose porous soil should be removed at this point, otherwise 
there will be a soft place which will soak up water and make a mud 
hole and also weaken the bank just below it. When an embank- 
ment is to be made across a swamp, bog, or marsh, the site should 
first be drained as thoroughly as possible. 

Perfect solidity should be the aim, and all necessary precautions 
should be taken to prevent or lessen the tendency of the bank to 
slip. To secure stability, embankments should be built in successive 
layers not more than 3 or 4 feet thick, and the vehicles conveying 
the materials should be required to pass over the bank, so as to con- 
solidate the earth. Specifications sometimes state that the layers 
shall be made concave, but this refinement is scarcely ever necessary, 
although it is well to see that the layers are never very much convex. 
Embankments are sometimes first built up in the center, and after- 
wards widened by tipping or dumping earth over the side; but this 
never should be allowed. 



ART. 1] CONSTRUCTION 91 

When embankments are to be formed on sloping ground, it may 
be necessary to plow the ground or to cut steps in a rocky surface 
to keep the filling from shding down the natural surface. In many 
cases where roads are to be constructed along steep slopes, it is 
found cheaper to use retaining walls (§ 192) to sustain the road 
upon the lower side and the earth-cut on the upper side than to 
cut long slopes or form high embankments. 

147. Improving Old Roads. Country roads may be improved 
in any of several ways: 

1. By changing the location, to secure better ahgnment or lower 
gradients. The method of doing this has been discussed in Art. 2, 
Chapter I. 

2. By cutting down the hills and filling up the hollows, to secure 
easier gradients. A hill may be cut down without seriously inter- 
fering with traffic by cutting one side of the roadway down a foot 
or two with drag or wheel scrapers (§ 154), and then turning traffic 
on this portion and lowering the other side, continuing to cut down 
each side alternately until the desired depth is reached. If the 
earth is deposited upon the embankment in the hollow, the traffic 
will consolidate the road as it is built up, which is very desirable. 

3. By laying tile and cutting open ditches, to improve the drain- 
age, as has been discussed in § 114-28. 

4. By re-forming the surface by the use of the scraping grader 
to improve surface drainage, as discussed in § 155-58. 

5. By adding sand or gravel to a clay road, or clay to a sand 
road, to improve the surface, as considered in Chapter IV. 

148. Road-building Machinery. In recent years there has 
been a great advance in the machinery employed in building earth- 
roads. The wheelbarrow was formerly much used for short hauls, 
but has been superseded by some form of drag scraper (§150) drawn 
by horses, and is never used now except for very small jobs, or in 
wet and swampy places. Formerly an embankment was constructed 
with plows arid drag-scoop scrapers (Fig. 17, page 92), while now it is 
built much more cheaply and better with either the scraping grader 
(Fig. 23, page 96), or with the elevating grader (Fig. 28, page 101). 
Years ago earth was thrown into wagons or carts by hand and hauled 
to its destination, while now it is moved with the two- or four- 
wheel scrapers (Fig. 21 or 22, page 95). Earth was formerly 
moved considerable distances with the drag scraper, while now the 
wheel scraper is employed. Formerly the surface of the excavation 
was finished with the drag-scoop scraper, while now it is done much 



92 EARTH ROADS [CHAP. Ill 

better and more cheaply with the tongue scraper (Fig. 18, page 
93) or the scraping grader (Fig. 23, page 96). 

There are a variety of plows, dump carts, wagons, etc., used in 
moving earth, which need not be considered here. The dump cart 
is much in favor in the New England States, but is never used in the 
Mississippi Valley. The steam shovel and dump cars afford the 
most economical method of handhng earth when the amount to be 
moved justifies the outlay for the plant; but as that would seldom 
be the case in highway work, this method will not be considered. 

149. Scrapers. Scrapers are generally used to move material 
after it has been loosened by plowing. There are two principal 
kinds — the drag and the wheel scraper. 

150. Drag Scrapers. There are three forms of the drag scraper 
— the scoop (Fig. 17), the pole-scraper (Fig. 18, page 93), and the 
Fresno scraper (Fig. 19, page 93). 

151. The drag-scoop scraper. Fig. 17, is sometimes referred to 
as the drag scraper or simply the drag, and also as the slip scraper or 

the shp. It is made in 
three sizes. The smallest, 
for one horse, has a capacity 
of 3 cubic feet; and the two 
larger sizes, for two horses, 
have a capacity of 5 and 
7 feet respectively. Some 
have metal runners on the bottom and others have practically a 
double bottom, both of which devices decrease draft and increase 
durability. 

The drag-scoop or slip scraper is much used for moving earth 
short distances; but with it there is difficulty in building a bank 
of uniform solidity, since each scraperful is deposited in a compact 
mass by itself, with low loose places between them. Nor is the 
shp scraper suitable for finishing an embankment, since the surface 
made with it is a succession of humps and hollows which is very 
tr3ang to drive over when dry, and when it rains the low places fill 
with water which speedily softens the remainder of the road, and 
finally produces mud holes. The pole or tongue scraper (§ 152) is 
much preferable for finishing the surface. 

The drag-scoop or shp scraper is sometimes employed in loading 
wagons. This is done by building an elevated platform under which 
the wagons are driven, and to the top of which the earth is drawn in 
a scoop scraper upon an inclined runway. In the middle of the plat- 




FiG. 17. — Dkag-Scoop Scraper. 



ART. 1] 



CONSTRUCTION 



93 



form is a hole through which the scraper is dumped. This arrange- 
ment of platform and runways is called a trap. 

152. The pole or tongue scraper, Fig. 18, is ordinarily used for 
leveling up the road surface in excavations, and is frequently 




Fig. 18. — Poll, or Tongue scraper. 

employed in preparing the subgrade for pavements. It may be 
used to transport earth short distances, but is not so good for this 
purpose as the scoop scraper. It is made in two sizes, 36 and 48 
inches wide. 

153. The Fresno scraper, Figs. 19 and 20 is the outgrowth of 




Fig. 19. — Fresno Scraper, Ready for Loading. 



experience in irrigation, and has some advantages over the com- 
mon scoop scraper. (1) The proportions are such that it is more 
readily loaded to its full capacity. (2) It distributes the earth on 



94 EARTH ROADS [CHAP. Ill 

the bank better, as it can be adjusted to deliver in layers from 1 to 
12 inches thick. (3) The runners make it more durable. (4) It 
is more easily loaded. (5) It will follow up a steep bank without 
dumping, and hence runways are not required. 

Fresno scrapers are made in three sizes, the cutting edge being 




Fig. 20. — Fresno Scraper, Dumped 

3 J feet, 4 feet, and 5 feet; and their respective capacity is 8, 10, and 
12 cubic feet. 

Under favorable conditions this form of scraper wiU push con- 
siderable earth along in front of it, and consequently the capacity 
is frequently stated as much greater than that given above. 

154. Wheel Scrapers. There are two forms of wheel scrapers, — 
those with two wheels and those with four. The two-wheel scraper 
consists of a steel box mounted on wheels and furnished with levers 
for raising, lowering, and dumping, Fig. 21, page 95. It is made in 
three sizes. No. 1, 2, and 3, having a capacity of 9, 12, and 16 cubic 
feet, respectively. Some manufacturers make an automatic front 
end-gate which adds materially to the load the scraper wiU carry, par- 
ticularly on a rough down-hill road. 

The four-wheel scraper is a steel box or scoop suspended from 
a frame supported upon four wheels, see Fig. 22, page 95. It is made 
in tVi/'o sizes, a half-yard and a yard capacity. It may be loaded by 
a snatch team or by steam power, — either a traction or a hoisting 
engine. The larger size is loaded with a 20 H.P. steam traction 



I 



/kRT. 1] 



CONSTRUCTION 



95 



engine or a 30-60 H.P. gasoline tractor, or by a hoisting engine; 
but when loaded, it is drawn by a two-horse team. The pan 




Fig. 21. — Two-Wheel Scraper, Filling. 




is raised and lowered by the tractive power. Work can be done 
cheaper with the four-wheel scraper than with the two-wheel 
scraper, because the former carries larger loads and also because it 
is self-loading and self-dumping. 
The four-wheel scraper has been 
called a self-loading and self- 
dumping wagon. 

The four-wheel or Maney 
scraper was first made in 1909, 
and has been used in the far 
west in railroad work. It is used 
extensively in preparing the sub- 
grade for pavements. 

155. Scraping Grader. There are several forms of scraping 
graders of the type shown in Fig. 23, which differ in minor details 
but all of which accomplish substantially the same work. Each 
consists of a frame carried on four wheels, supporting an adjustable 
scraper-blade, the front end of which plows a furrow while the rear 
end pushes the earth toward the center of the road or distributes it 
uniformly to form a smooth surface. The blade can be set at any 
angle with the direction of draft, or at any height ; and it may also 
be tilted forward or backward. This machine will work in almost 
any soil — even where a plow will not. It is hauled by horses or 
traction engine, usually the former, and makes successive rounds 



Fig. 22. — Four-Wheel Scraper. 



96 



EARTH ROADS 



[chap. Ill 



or cuts until the desired depth of ditch and crown of road is ob- 
tained. 

This machine is often called a road grader and sometimes a blade 
grader; but it is here designated as a scraper grader to distinguish 




Pig. 23. — Scraping Grader, 

it from the elevating grader (§ 161). The scraping grader is an 
important machine in both the construction and the care of earth 
roads. As an instrument of maintenance it has been called a road 
hone, but could more properly be called a road plane. 

Fig. 24 to 27, pages 98 to 99, show the various kinds of con- 
struction work that may be done with this type of machine. For 
a discussion of the work of this machine in maintenance, see § 208-11. 

Various devices are employed to neutrahze the lateral resistance 
of the earth to being pushed side wise by the blade. In some types 
the whole rear end of the machine may be thrown to one side or the 
other by operating a hand-wheel; in other forms the rear axle is 
shifted lengthwise so that one wheel may bear against the unplowed 
bank of the ditch; in other cases either rear wheel can be moved in 
or out independently; in still other types either the front or rear 
wheels or both may be set at any inclination by operating a hand- 
wheel; and in other forms the wheels have a flange which cuts into 
the earth and resists the lateral thrust. 

The scraping grader is of inestimable value in constructing 
Qarth roads, as it does the work better and much cheaper than it 
ran be done either by hand or with plows and scrapers. The work 
done with the scraping grader is also superior to that done with 
plows and drag scrapers, since the plow cuts deeper in some places 



1 



ART. 1] CONSTRUCTION 97 

than others and these places are left full of loose earth and soon 
form holes which catch and hold water. 

156. There are scraping or blade graders on the market having 
only two wheels, and also those having no wheels; but such machines 
are neither conomon nor efficient. They have been superseded by 
the road drag (§ 206). 

157. Operating the Scraping Grader. To build a road with the 
scraping grader, first plow a light furrow with the point of the blade, 
where the outside of the ditch is to be (see Fig. 24, page 98). To 
make the blade penetrate hard or stony ground, elevate the rear end 
considerably and use only the point. On the second round, with 
the front and rear wheels in Hne (see Fig. 25), drive the team so 
that the point of the blade will follow the furrow made the first 
round, plowing a full furrow with the advance end of the blade, and 
dropping the rear end somewhat lower than before. The third tim.e 
round, move the earth previously plowed oyer toward the middle of 
the road. In moving the earth toward the center of the road, 
elevate the rear end of the blade to allow the earth to distribute 
under it, so as to build the road at the side of the proper crown 
before fiUing the center; and if the machine slides sidewise instead 
of pushing the ridge of earth toward the center, either slue the 
whole rear end of the machine toward the center, or move one hind 
wheel or the whole rear axle laterally until the rear wheel bears 
against the bottom of the unplowed bank at the ditch, or incline 
the rear wheels, according to the construction of the machine. 
Finally, return to the ditch and plow it out deeper, moving the earth 
over toward the middle whenever as much is plowed as the machine 
can move at once. Repeat this until the ditches are of the proper 
depth, and the road as full and round as required. 

A ridge should not be left in the middle of the road. Usually a 
skillful handling of the machine will prevent the formation of such 
a ridge by elevating the rear end of the scraping blade, thus allowing 
the earth to lose out under it as the center of the road is approached. 
If the road is very rough, it may not be possible to fiU all the ruts 
without at some places forming a ridge in the center of the road. 
If the ridge is formed, it can be flatted down by setting the blade 
square across the road and allowing the earth to flow under it; or 
with most machines the center ridge can be leveled down by revers- 
ing the blade and using the back of it. 

If the ground where a road is to be constructed is covered with 
weeds and grass, it should be cleared by burning or by mowing and 



98 



EARTH ROADS 



[chap. Ill 




Fig. 24. — Sceaping Gbader Making First Round. 




Fig. 25. — Scraping Gbader Making Second Round. 



ART. 1] 



CONSTRUCTION 



99 




Fig. 26. — Sckaping Grader Plowing between Front Wheels. 




Fig. 27. — Scraping Grader Cutting awat Old Bank. 



100 EARTH ROADS [CHAP. lU 

raking. With sod ground the best road can be obtained by first 
cutting the sod as thin as possible and moving it to the center of the 
road, and then going back to the ditch and continuing the grading 
as described above. To cut a thin sUce of sod, the scraper blade 
should be as sharp as possible. When the ground to be moved is 
covered with sod or weeds, some operators make the first cut on the 
inside of the ditch and at each successive round cut a Httle farther 
out, thus distributing the sod through the earth forming the road- 
way. This requires too much cutting with the unsharpened end of 
the blade, and is therefore not as good as the method described above. 

158. It is best not to put more than 4 to 6 inches of loose earth 
into the road at one working, as that is aU that can be thoroughly 
packed by traffic. If a greater amount is thrown up at one time, 
the bottom of the grade will remain soft and cause the road to cut 
into deep ruts as soon as the top has become thoroughly soaked by 
rain. As far as possible the grading should be done early in the 
summer, giving ample time for the loose earth to settle and pack 
before the fall rains. If worked in the fall, there should never 
be more than 4 inches of loose earth put upon the road at one 
working. 

If the maximum amount of earth is to be placed upon the road 
at once, it is wise to roll each successive layer with as heavy a roller 
as is available or as a team can draw, as otherwise traffic will con- 
soHdate only the surface, and the bottom of the grade will long 
remain soft and spongy. 

159. The scraping grader is usually drawn by four or six horses, 
depending upon their size, and the character and condition of the. 
soil. One man can operate the machine, and one or two men are 
required to drive. 

A traction engine is sometimes used; and it is a better power, 
since it gives a steady draft and does not need to stop to rest. At 
certain seasons of the year, the traction engine is the cheaper power, 
and at other times horses are the cheaper, depending upon the re- 
quirements of horses for farm work and the demands for the trac- 
tion engine in threshing and shelling. 

160. The cost of building an ordinary prairie road with horse- 
power with this machine is about $30 to $40 per mile, with a width 
of 30 or 35 feet and a crown of 6 inches above the natural surface. 
The first is the cost when there is no sod, and the second when there 
is a stiff sod. A second 6 inches may be added for about $30 per 
fnile. 



ART. 1] 



CONStRUCTiON 



101 



If the ground is very dry and hard, another team and driver will 
be required, and the above prices may be nearly doubled. 

161. Elevating Grader. The best known form of the elevating 
grader is shown in Fig. 28. It consists of a frame resting upon four 
wheels, from which is suspended a plow and a frame carrying a 
wide travehng belt. The carrier is built in sections and its height 
is adjustable. The larger carrier will dehver earth 14, 17, 19, or 22 
feet horizontally and 8 feet vertically from the plow; while the 
smaller size will dehver 14 and 17 feet horizontally and 7 feet verti- 
cally. The smaller machine is designed for highway work. The 




Fig. 28. — Elevating Grader. 



plow loosens the soil and throws it upon the traveling inclined belt, 
which delivers it upon the embankment direct or into wagons. 

This is an exceedingly effective machine for building open ditches, 
earth embankments, or filhng wagons. By changing the length of 
the carrier and by properly distributing the earth, the machine will 
build either a broad low embankment from a narrow deep cutting, 
or a narrow high embankment from a broad shallow cutting; or 
the machine will excavate a deep narrow ditch with flat spoil banks, 
or a shallow ditch with narrow spoil banks. This machine is espe- 
cially adapted to building earth roads in a prairie country, for 
which purpose it has been very largely used. 

The large machine is usually propelled by twelve horses — eight 
in front and four behind, — and the smaller by eight in front. Often 
a traction engine is cheaper than horses. One man can operate the 
machine; and at least two men, and usually three, are required to 
drive the larger machine, but usually two drive the smaller one. 



102 



EARTH ROADS 



[chap. Ill 



162. Operating the Elevating Grader. To build a new road of 
the sections shown in Fig. 11 and 12, page 82, first mark by stakes 
a Hne 10 feet on each side of the center of the proposed road. With 
the machine arranged to throw the earth 17 feet horizontally, drive 
along the left-hand row of stakes and back on the other side of the 
road in the same way. The streams of earth as delivered will overlap 
5 or 6 feet. Start the machine on the second round with the right- 
hand forward wheel in the furrow of the previous round, and complete 
the round. A harrow should follow the machine to break up the 
sod and level the bank. Continue to make rounds until the ditches 
are as wide as desired. 

Commence the second plowing by bringing the left-hand wheel 
of the machine to the left-hand edge of the first furrow cut, which 
brings the plow one furrow to the left of the point of commencing 
the first plowing, and keep this relative position while making this 
round. Make the second round with the left-hand forward wheel 
in the furrow of the previous round; and continue to make rounds 
until the outside of the ditch is reached again. For the best results 
a harrow and roller — the heavier the better — should follow the 
grader during the second and subsequent rounds — see Fig. 29. 

When the second plowing has been completed, the grade will be 




Fig. 29. — Elevating Grader Building Earth Road. 



high and narrow; and therefore the carrier should be shortened to 
14 feet. Then start the machine so that the plow will take a furrow 



ART. 1] CONSTRUCTION 103 

from the center of the ditch, and continue the third plowing, as 
described above for the first and second, to the outside of the ditch. 
For the fourth plowing take a couple of furrows from the outside of 
the excavation to deepen the ditch. 

The final result should be about as in Fig. 11 or 12, page 82. Most 
operators, however, leave a berm at the inside edge of the ditch 
(Fig. 37, page 122), which is undesirable since it interferes with the 
operation of the scraping grader in maintaining the road. 

163. For loading wagons, the carrier is arranged to deliver at 17 
or 19 feet horizontally from the machine, the wagons are driven so 
that the earth falls from the carrier into the wagon, and both move 
at the same speed until the wagon is loaded; and then the grader 
slows down while the loaded wagon drives out and an empty one 
drives in. Common wagons with dump boards are not so easily 
loaded as the usual dump wagon, since they are narrower and longer. 
It is customary to estimate three dump wagons for the first 100 feet 
of haul, and an additional wagon for each 100 feet thereafter. 

164. Cost of Earthwork. Of necessity, general estimates of 
the cost of earthwork can not be very exact, since the cost wiU vary 
with the condition of the soil, the wages, the hours constituting a 
day's work, the relative amount paid for supervision, the effective- 
ness of the supervision, the facilities for preventing one part of the 
crew from interfering with the work of another, the proper adjust- 
ment of the number of shovelers per wagon or cart, or of scraper 
holders to scrapers, etc. The following data have been checked by 
engineers and contractors of wide experience and are believed to be 
reasonably reliable.* 

165. In the analysis of the cost of earthwork to follow, the price 
for a man will be assumed to be $1.50 per day of 10 hours, and that 
for a team and driver $8.50 per day. These were the usual wages 
formerly paid by contractors, which are the prices to be considered 
here; for if the work is done under the labor-tax system ordinary 
estimates will not apply (§ 51-52), and if the farmer hires out to 
do the work of a teamster he usually demands the ordinary pay for 
that class of work. These were about the prices current for a number 
of years in a number of states, before the rise of prices incident to 
the Great European War. Of course, if wages are greater than as 
stated above, the following prices can be changed proportionally. 

166. Cost with Scraping Grader. In prairie soil, two men and 

* For an instructive discussion of methods of Handling Earth in Road Construction, see an 
article by Chas. R, Thomas in Engineering and Contracting, Vol. 47 (1917), pp. 406-08. 



104 EAKTH ROADS [CHAP. Ill 

four horses with a scraping grader can build a mile of road 36 feet 
wide from inside to inside of ditch with a crown of 6 inches at the 
center after being compacted, for $30 to $40, which is equivalent to 
if or 2 J cents per cubic yard. The first is the cost when there is 
no sod, and the last when there is sod. The cost for a crown of 12 
inches will be about $70 per mile, or If cents per cubic yard. The 
above prices do not include interest, or wear and tear of grader, 
which would be about ^ cent per cubic yard. 

In hard soil requiring an extra team and hence another driver, 
add one half to the above prices. 

167. Cost with Elevating Grader. The elevating grader, Fig. 28 
and 29, pages 101 and 102, will, in light prairie soil, deposit on a road 
1,000 cubic yards per day of 10 hours; and will load into wagons 
500 yards per day. The outfit required is: seven two-horse teams 
at $2.50 each plus 2 drivers at $2.00 each plus 1 operator at $2.00 and 
1 at $2.50 = $29.50. For the earth deposited on the road this is 2.9 
cents per cubic yard, and for that loaded into wagons 5.8 cents, 
exclusive of interest, depreciation, and administration. 

168. Cost with Drag-Scoop Scraper. Drag scrapers are admirably 
adapted for borrowing at the sides of embankments and for wasting 
from cuts or ditches, and also for opening the mouth of large cuts; 
but are not economical except for short distances. There is no 
danger of the scraper getting out of order until it is worn out and 
unfit for use, and the manner of using it is quickly learned by any 
one. Drag scrapers are made in three sizes having a capacity of 
3, 5, and 7 cubic feet, respectively; but it must not be assumed 
that each scraper will carry to the embankment an amount equal to 
its rated capacity, since in the first place it is difficult to completely 
fill the scraper, and in the second place the scraper carries loose 
earth which will shrink about 25 per cent when compacted in the 
embankment. Unless the soil is very loose and easily loaded, it is 
not safe to assume that each trip of the scraper will make of com- 
pleted embankment more than one half of its rated capacity. The 
larger size is most economical, but the relative advantage is not 
proportional to the size, since the larger size is not as easy to handle 
nor as easy to fill. Scrapers should be used in gangs of not less 
than six to decrease the cost of loading, superintendence, spreading, 
etc. 

169. Cost of Loosening. Sand or sandy loam can be scraped 
without plowing. In loam a two-horse team and plow will loosen 
400 cubic yards per day, at a cost of $3.50 for team, plow, and driver, 



ART. 1] CONSTRUCTION /105 

and $1.50 for the plow holder, making a total of $5.00, or Ij cents 
per cubic yard. Sometimes the driver can also hold the plow, in 
which case loosening will cost about 1 cent per cubic yard, since the 
team will not do quite as much work as when there is a plow holder 
and also a driver. If the ground is hard it will be necessary to add 
another team and also a man to " ride " the beam of the plow. If 
the ground is not very hard, this force will loosen 400 cubic yards 
per day at a cost of 2.1 cents per yard. 

170. Cost for 25-foot Haul. The cost of building an embank- 
ment from a borrow pit at the side of the road will first be considered. 
For a 60-foot right-of-way and a light embankment, the length of 
haul or " lead " from center of gravity of the fiU to the center of 
gravity of the cut will be about 25 feet. This distance v/ill be a 
little more or a little less according to the height and width of the 
bank, and the width reserved for sidewalk; but slight difference in 
length of short hauls make comparatively little difference in the 
cost of moving the earth, because in the first place a considerable 
part of the cost of hauling is due to time consumed in turning and 
loading, and in the second place the cost of transportation is only 
about half the total cost of moving the earth. 

On the road, an ordinary team will travel 220 feet per minute 
(2| miles per hour), but in scraping considerable time is consumed 
in turning, waiting to load, etc., and besides, the distance traveled is 
more than that from the center of cut to the center of fill; therefore 
the ordinary speed of the team is no guide in this connection. 
Experience shows that a team will use from a minute to a minute 
and a half in making a round trip at the above distance, or, say, li 
minutes per trip. A foot vertically is equivalent to 10 to 25 feet 
horizontally (see § 77), and in estimating the length of haul this 
fact must be taken into account. 

Using the large scraper, a scraperful will make 3 J cubic feet 
of compacted embankment, or will require eight trips per cubic 
yard. Therefore a team will place a yard of earth in the fill every 
10 minutes, or 6 yards per hour and 60 yards per day. In light loose 
earth, where it is easy to fill the scrapers full, a team may make 70 
yards; but if the ground is hard, or obstructed with roots and grass, 
50 yards may be the maximum. Assuming a day's work to be 60 
yards, the cost of hauUng is $3.50 -^ 60 = 5.83 cents per cubic 
yard. 

One man will hold and fill the scraper for two teams at a cost of 
$1.50 -^ (2 X 60) = 1.25 cents per yard. One man on the dump 



106 EARTH ROADS [CHAP. Ill 

will distribute and level the earth deposited by six teams, at a cost 
of $1.50 -^ (6 X 60) = 0.4 cents per cubic yard. One foreman 
will be required at, say, $2.50 per day; or $2.50 -^ (6 X 60) = 0.69 
<jents per cubic yard. For wear and tear of scraper we may allow 
10 cents per day for each, or 60 cents for the lot; and for wear of 
plow and cost of sharpening, say, 30 cents, making a total of 90 cents 
or 0.25 cents per cubic yard. In very hard ground the above prices 
may be doubled. 

The total cost of moving earth 25 feet will then be as iq Table 18, 
page 108. 

171. Cost for 50-foot Haul. We will next consider the cost for a 
50-foot haul. At this distance a scraper holder can fill for three 
teams. Each team can put in about 50 cubic yards per day. The 
other items will be substantially as for a 25-foot haul, and the total 
cost will be as in Table 18. 

172. Cost for 100-foot Haul. Each team will make a trip in 
about 2J minutes, and will put in 40 cubic yards per day. The 
total cost will be as in Table 18. 

173. Cost for 200-foot Haul. At this distance a scraper holder 
can fill for four teams. Each team will make the trip in about 3^ 
minutes, and put in about 35 cubic yards per day. The total cost 
will then be as in Table 18. 

174. Cost for Hard Ground. If the ground is so difficult to plow 
as to require a second team and a man to ride the beam, add 1 or Ij 
cents to the values in Table 18 for the extra cost of loosening; and 
add, say, one fifth to the cost of hauling to allow for the fact that 
in hard ground the scrapers are not as well filled as in loose fight 
soil. Also add one half to the above estimated cost of wear and 
tear. The results for hard ground are then as in Table 18. 

175. Cost with Two-Wheel Scrapers. Two-wheel scrapers are 
excellent for hauling earth distances up to 600 or 700 feet. They 
are made in three sizes. No. 1, 2, and 3, having a capacity of 9, 12, 
and 15 cubic feet, respectively. With No. 1 the team fills its own 
scraper, while with No. 3 an extra team (a snatch team) is required 
to fiU the scrapers reasonably full; and unless the ground is very 
loose and Ught an extra team is required to fill No. 2. Most con- 
tractors use either No. 1 with a single team or No. 3 with a snatch 
team. It usually takes about five loads with No. 1 to make a cubic 
yard in place; four, with No. 2; and three, with No. 3. 

176. Cost for 100-foot Haul. It is assumed that the scrapers 
will be worked in a gang of six, which will require one foreman, one 



ART. 1] CONSTRUCTION 107 

plow, three scraper holders, and one man on the dump. The 
expense for these items will be the same as for the drag scrapers, 
and are so entered in Table 19, page 109. At this distance a trip 
will occupy 2i minutes, and a yard will be deposited every 10 min- 
utes, or 60 yards per day, at a total cost $3.50, or 5.83 cents per 
cubic yard for hauling. 

The wear and tear is computed on the assumption that a scraper 
will last for 200 days' continuous work, mailing a cost for deprecia- 
tion and repairs of, say, 20 cents per day per scraper. The wear 
and tear on the plow will be estimated at 30 cents per day. The 
total cost will then be as in Table 19. 

177. Notice that the cost for 100 feet with the two- wheel scraper 
is 9.99 cents per cubic yard, while with the drag scraper for the same 
distance it is 12.67 cents. The difference is in the cost of hauling, 
which is due to the difference in the capacity of the scrapers. 

178. Cost for 200-foot Haul. A trip will be made in about 4 
minutes, and each scraper will put in 50 cubic yards per day. The 
three scraper holders can fill an additional scraper, making nine 
in all. The cost will then be as in Table 19. 

179. Cost for SOO-foot Haul. In this case another scraper can 
be added, making four scrapers to each scraper holder. A trip can 
be made in about 5J minutes, and each team will move 45 yards 
per day. The cost will be as stated in Table 19. 

180. Cost for 4:00-foot Haul. It is difficult to determine the 
most economic distance for each size of scraper, since the several 
sizes are seldom available for making the test. However, at 300 
feet, the cost with a No. 2 scraper is about the same as with a 
No. 1 at 200 feet; and at 400 feet the cost with a No. 2 is about the 
same as with a No. 1 at 300 feet. But at 400 feet a No. 3 is more 
economical than a No. 2. 

A snatch team is required in filling No. 3 scrapers. The extra 
force acquired by using the extra team completely fills the scraper, 
and also packs the load so that it is less liable to spill than when 
loaded by a single team. For this distance it is mOst economical 
to work the scrapers in a gang of eight; and two men will be re- 
quired to hold the scrapers while being filled. Each team will put 
into place 45 cubic yards, or 360 for the gang. The total cost will 
be as shown in Table 19. 

181. Cost for Other Distances. For each additional 100 feet of 
lead, add 1 cent per cubic yard to the cost of haul; and the total 
cost will be approximately as shown in Table 19. 



108 



EARTH ROADS 



[chap. Ill 








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CONSTRUCTION 



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110 EARTH ROADS [CHAP. Ill 

When the amount of earth to be moved is considerable and the 
length of haul is great, something must be allowed for keeping in 
repair the road over which the earth is transported. A wheel 
scraper is prone to wear a series of humps and hollows along the 
road it traverses, and these must be kept in subjection, if the work 
is to be done at reasonable cost. The proper allowance will vary 
greatly with the soil, the weather, etc. Trautwine recommends 
0.1 cent per cubic yard per 100 feet for this expense. 

182. It is difficult to determine at what distance wagons should 
supersede two-wheel scrapers; but usually the economic limit for 
two-wheel scrapers is 600 to 800 feet, and it is seldom wise to use 
such scrapers beyond 800 feet — unless they are at hand and wagons 
are not.* 

183. Cost with Four-Wheel Scrapers. The cost of moving earth 
with the four-wheel scraper is not well estabhshed. With enough 
scrapers to keep the loading engine reasonably busy, the cost of 
power for loading — operator, fuel, rent, etc., — will be about 2 or 
3 cents per cubic yard, depending upon the hardness of the soil. 
The saving in loading is 5 to 6 cents over that of wagons — see 
§ 184. 

184. Cost with Wagons. It will be assumed that the wagons are 
filled by hand, that they are used in gangs of nine, and that the haul 
is 700 to 800 feet. If the roads are level and fairly smooth, a load 
will make about IJ cubic yards in place; and with ordinary roads, 1 
yard will make a load ; but if the roads are soft and steep, | of a yard 
may make a load. The amount a team can deliver will vary greatly 
with the time consumed in waiting to load and in loading. With 
short wagon-hauls and well-organized work, half of the time is thus 
consumed, and often much more is thus consumed. The time of 
the wagon while loading should be considered as a part of the cost 
of loading, and this will be discussed more fully in the next para- 
graph. For the above distance, the round trip will consume 15 
minutes; and assuming a yard as a load, each wagon will dehver 
50 cubic yards per day, at a cost of 7.00 cents per cubic yard for 
hauling. 

There is very great variation in the amount of earth a shoveler 
will load in a day. In well managed work, the shovelers are not 



* For the results of an elaborate time study of cost of moving various kinds of soils dif- 
ferent distances with two-wheel scrapers and Fresno scrapers, see Engineering and Contracting, 
Vol. 41 (1914), pp. 629-36. 



ART. 1] CONSTRUCTION 111 

actually engaged in loading much more than half of the time; while 
under poor management, they do not really work half of the time. 
With short intervals of rest equal to the working time, a man should 
load, in a day of 10 hours, 20 cubic yards of Ught sandy soil, 17 
yards of loam, and 15 of heavy soil — provided all are loosened by 
plowing or picking. Usually five or seven men are set to load a 
wagon — two or three on each side and one at the rear. Seven men 
will load a wagon with loam in 5 minutes, 8 minutes will be con- 
sumed in traveling to and from the dump, 1 minute in dumping 
and 1 minute in getting into and out of the cut — making in all 15 
minutes for a round trip; and therefore the cost for wagon and 
team is 8.75 cents per cubic yard, as above. In this case the team 
works only about half the time. If only five men are engaged in 
loading a wagon, 7 minutes will be consumed in loading, and the 
time for a round trip will be 17 minutes, and each wagon will deliver 
only 35 cubic yards, making the cost 10 cents per cubic yard. In 
this case, the team really works less than half the time. If the 
men shovel only 12 to 15 cubic yards each, as is very common, the 
loss by the wagon's waiting for a load is considerably more than 
above. The proper number of men to be set to loading a wagon 
depends upon the relative wages of shoveler and wagon, upon the 
length of the haul, and upon the quantity loaded per day per man. 
Usually seven shovelers are employed to each wagon, but this 
number is not enough to secure the greatest economy. In the fol- 
lowing estimates it will be assumed that nine shovelers are em- 
ployed to each wagon. At the above distance, nine shovelers, each 
loading 17 yards per day, will be required to keep three wagons 
going, each of which deposits 45 cubic yards per day. The cost of 
loading will then be 8.8 cents per cubic yard. 

The cost of leveling the dump is small, if dump wagons are used 
and the earth is dumped over the end of the embankment or wasted ; 
and it may be taken the same as for scrapers, i. e., at 0.40 cents 
per cubic yard. But dump wagons are so heavy and expensive 
that they are seldom used; and if ordinary wagons with dump 
boards are employed, the expense for labor on the dump will be 
about three times as great as above, or, say, 1.20 cents per cubic 
yard. 

The driver furnishes his own wagon, and hence no account is 
taken of the wear and tear of it. There should be a small allowance 
made for the wear and care of shovels, say, 0.1 cent per cubic 
yard. 



112 



EARTH ROADS 



[chap. Ill 



The total cost of moving earth 700 to 800 feet with wagons, 
then, is as follows: 

1. Loosening 1 . 25 cts. per cu. yd. 

2. Shoveling 8.80 

3. Depreciation of shovels 0.10 

4. Hauling 700 to 800 feet 7.00 

5. Helper on dump 1 . 20 

6. Superintendence . 69 

7. Water boy 0.16 



Total cost 18.20 



( ( ( c 



185. For longer distances add 1 cent per cubic yard for each 
100 feet of distance — the usual charge for over-haul. 

186. Other Methods. When the haul is more than 600 or 800 
feet, and when the amount of work to be done is sufficient to justify 
the initial expense, it is more economical to use portable track and 
small dump cars than to use wagons. However, such conditions 
seldom occur in wagon-road construction. 

187. Finishing the Slopes. In addition to the elements of 
cost discussed above, there is always some expense in levehng off 
the bottom of the cut, in digging ditches, in trimming up the slopes 
of embankments and excavations, and in cutting a catch-water at 
the top of the slope in excavation. The cost of these items will 
very greatly with the degree of finish required and also with the 
depth of the cut or the fill; and it may amount to 0.25 or 0.50 of 
a cent per cubic yard. If the bottom of the cut can be leveled off 
with the scraping grader, and if the ditch also can be made with 
this machine, the cost of this item will be considerably reduced. 

188. Profits and Administration. The proper allowance under 
this head will vary according to the magnitude of the work, the 
risks involved, etc.; but will usually be 5 to 15 per cent. Out of 
this the contractor must pay the expense of assembling the plant, 
the cost of tool house, the wear and tear on small tools, interest 
on investment, profits, etc. 

189. Bridges. This subject will not be considered here, since 
the space available is not sufficient, and since there are a number 
of elaborate treatises on bridges. None of these, however, gives 
an adequate treatment of the very small highway bridge, or fairly 
represents current practice for moderate spans. 



ART. 1] CONSTRUCTION 113 

190. Waterways. The determination of the amount of 
waterway required for any particular bridge or culvert is a matter 
of importance. Although the problem does not admit of an exact 
mathematical solution, it requires intelligent treatment. For a 
discussion of this subject, see pages 564-69 of the tenth edition of 
author's Masonry Construction.* 

191. Culverts. For a discussion of the cost and method of 
construction of culverts — wood box, vitrified pipe, cast iron pipe, 
stone box, and masonry-arch culverts, — see the author's Masonry 
Construction, pages 569-605. '^ 

One common defect of earth roads is that culverts are made too 
short, which concentrates the traffic upon the portion of the road 
usually least able to bear it. A short culvert may be permissible 
when the cost per unit of length is great, but the defect is common 
where this cost is quite small. 

192. Retaining Walls. Retaining walls are masonry struc- 
tures employed to support the sides of roads on hillsides or in places 
where land for the ordinary earth slopes is not readily obtainable. 
For a discussion of retaining walls, see the author's Masonry Con- 
struction, pages 489-534.* 

193. Guard Rails. Roads on steep hillsides or on high em- 
bankments, and particularly on sharp curves in mountain roads, 
should be protected to insure vehicles against the possibiUty of 
faUing down the slope. In Europe such protection is usually 
afforded by a stone wall, or by stone posts set at frequent intervals. 
In this country the usual protection is by means of wood posts and 
wood guard rails. The description of the guard rails used on the 
state-aid roads in Massachusetts is as follows: " Posts of cedar, or 
other wood which endures well in the soil, are set at intervals of 8 
feet, and 1 foot in from the edge of the embankment. These posts 
are planted to the depth of 3 feet, and project for 3 feet 6 inches 
above the ground. The top of this post is transversely notched, so 
as to receive one half of a rail 4 inches square. Half-way down, 
the post is notched to receive another rail 2 by 6 inches in size. 
These rails, preferably of planed spruce wood, are spiked to the 
posts. To insure the better preservation of the wood and it 
visibility in the night-time, it is painted with two coats of oil paint 
of some light color." For a diagram of this guard rail, see Fig. 52, 
page 198. 

* A Treatise on Masonry Construction, by Ira O. Baker, 745 +xv pp., 6X9 inches, cloth, 
10th edition. John Wiley & Sons, New York. Price $5.00. 



114 EARTH ROADS [CHAP. Ill 

The Massachusetts Highway Commission wherever practicable 
widens the base of the embankment until a slope of 1 to 4 is ob- 
tained, and then dispenses with the guard rail. This plan is believed 
to be more economical, and to give a better appearance. 

194. Guide Posts. Some states, by statute, require guide 
posts at all intersections; and their value to the occasional traveler 
is sufficient to justify the expense. The guide post may be a plain 
post, supporting near its top a board upon which is the name of 
the place reached by the road, with figures showing the distance, 
and a 2^^ to show^ the direction. 

195. Artistic Treatment. Engineers are accustomed to 
study chiefly or only the economic side of construction, and are 
therefore Hkely to neglect the artistic treatment of the highway. 
In the attempt to beautify the roadside, it may be necessary to sac- 
rifice a little of utiHty to secure a pleasing effect. Masses of fohage 
and shade add beauty to the roadside, but tend to keep the traveled 
way damp — ^usually the bane of good earth roads. Trees are a 
necessary adjunct to a beautiful highway, but are anything but a 
benefit to the traveled way. If beauty is desired at the expense of 
utiHty, highways can scarcely be too much shaded by over-arching 
boughs. However, a happy medium wiU suflace in most places. 

The varieties of trees suitable for the ornamentation of highways 
are almost infinite. The elm, with its graceful arching branches 
and delicate lace-hke fohage, is not surpassed; and the hard maple 
and the oaks are very handsome for this purpose. The walnut, the 
butternut, the hickory, the beech, the poplar, and the pine, ranging 
from the most dehcate to the most somber and rugged, are aU more 
or less adapted to particular requirements and circmnstances. 
Trees such as willow, the roots of which spread extensively or seek 
water vigorously, should not be permitted to grow near tile drains, 
as the small roots frequently entirely obstruct the tile. Trees 
should not be planted close to the traveled way, but near the edge of 
the right-of-way, or if possible on the private property bordering 
the right-of-way. 

196. The roadside fences are usually the property of the adjoin- 
ing land owner, and may mar or beautify the landscape. The 
hedge rows of England and the stone fences of New England are all 
that can be desired for appearance; but in localities where there is 
much snow they catch the drifting snow and so obstruct the high- 
way. The only thing favorable to the appearance of the common 
wire fence is that it is inconspicuous. 



i 



ART. 2] MAINTENANCE ' 115 



Art. 2. Maintenance 

197. Proper maintenance is as important as good construction. 
A distinction should be made between maintenance and repairing. 
The former keeps the road always in good condition; the latter 
makes it so only occasionally. If the road is not properly main- 
tained, it deteriorates in a geometrical ratio. A small depression 
fills with water and soon becomes a mud hole which travel makes 
deeper and deeper; or an obstructed side ditch forces the water to 
run down the center of the road, and gullies out the surface. A 
defect which could be remedied in the beginning with a shovelful of 
earth and a minute's time, if neglected may require a wagon load of 
earth or an hour's time, besides being in the meantime an annoj^ance 
or a damage to travel. The better the state in which a road is kept, 
the less are the injuries to it by ordinary travel and the weather. 

198. Destructive Agents. The agents tending to destroy 
the road are: water, narrow tires, the tracking of the front and rear 
wheels, the horse not being hitched before the wheel. 

199. Water. Water is the natural enemy of good earth roads. 
The chief object of maintenance should be to keep the surface smooth 
and properly crowned so that rain will be shed into the side ditches. 
These should be kept open so that the water may be carried entirely 
away from the road. This subject is fully considered in § 205-15. 

200. Narrow Tires. It is desirable that a wagon in passing 
over the road should help to make or preserve it, and not to destroy 
it; and therefore as far as the road is concerned, within reason- 
able limits, the broader the tire the better. 

Tables 3 and 4, pages 15 and 16, show the relative tractive resist- 
ance of broad and narrow tires. Although there is not much differ- 
ence between the tractive power of broad and narrow tires, the latter 
are much more destructive on any road, particularly on an earth 
one. But in deciding upon the proper width of tire, there are other 
factors besides the tractive resistance and the preservation of the 
road, that must be considered. 

If wagons were employed only upon the public highway, it 
might be wise to use wide tires and sacrifice some tractive power 
for the benefit of the roads. Other things being equal, a wagon 
with broad tires is not so easily managed as one with narrow tires. 
To be equally easy to turn, the broad-tired wagon should have a 
narrower bed, or a longer front axle, or a smaller front wheel. In 



116 EARTH ROADS [CHAP. Ill 

Europe it is customary to adopt the smaller front wheel, which is 
very destructive of the broken-stone roads so common in that 
country. Increasing the length of axle interferes with getting the 
wagon up to cribs, warehouses, etc., and increases the difficulty in 
going through gates, passing buildings, etc. It is not clear that laws 
should be passed regulating the width of tires, many claims to the 
contrary notwithstanding. 

" The best argument against the enactment of laws concerning 
broad tires is found in the fact that the numerous and long-enforced 
EngUsh statutes on this matter have of late years been abrogated, 
a century of experience having shown that they are difficult to 
administer and generally disadvantageous." The Massachusetts 
Highway Commission, after an elaborate discussion of the subject,* 
says: "It is a matter of doubtful expediency to endeavor, in the 
present state of our highways, by general legislation to control the 
width of tires or the diameter of wheels." 

201. Many European countries have laws regulating the width 
of tires. In England for 100 years the law required 1 inch of tire 
for each 500 pounds of load, but all general laws in that country 
regulating the width of tires have been repealed. In France the tires 
of market carts vary from 3 to 10 inches in width, being generally 
from 4 to 6 inches, with the rear axle about 14 inches longer than the 
forward one. 

In this country a number of the states have statutes concerning 
the width of tires, many of which take the form of a rebate, either 
cash or part of the road tax, to those using tires of a prescribed 
width. The following is the legal width in Ohio for vehicles using 
gravel or broken-stone roads: 

Minimum width of tire for load of 2,500 to 3,500 lb 3 inches 

3,500 '' 4,000 '^ 3^ " 

4,000 '' 6,000 '' 4 " 

" " " 6,000 " 8,000 '' 5 " 

** " " 8,000 or more" 6 '' 

According to wagon manufacturers about 60 per cent of the 
wagons used on country roads have tires IJ to If inches wide, those 
of the remaining 40 per cent being 2 to 4 inches. The broad tire is 
of comparatively recent introduction on rural roads in this country. 

202. There is greater justification for hmiting the load per unit 
of width of tire on pavements than on earth roads, since with the 

* Report of the Massachusetts Highway Commission for 1893, p. 56-62. 



ART. 2] MAINTENANCE 117 

latter the damage is not so great and can be more easily repaired. 
For a discussion of limiting loads on pavements, see § 39. Notice, 
however, that these regulations apply only to loads heavier than any 
likely to traverse earth roads. 

203. Equal Axles. Since with equal axles the hind wheel follows 
in the track of the fore wheel, it increases the depth of the rut, and 
consequently increases the destructive effect of the wagon upon the 
road. The remedy would be to make the lengths of the two axles 
unequal, but this would make the wagon more difficult to manage 
and would also increase the tractive resistance. The advantage of 
not permitting one wheel to exactly follow another, is shov/n by the 
fact that there are no ruts at a corner or a sharp turn in the road; but 
it is not practicable to secure this advantage generally, either by 
m-aking the two axles of unequal length or by preventing a wagon 
from traveling in the ruts already made. 

204. Horse not Hitched before Wheel. On broken-stone roads, 
the horses' feet loosen fragments of stone, which tends to destroy 
the surface; and if the horses were hitched directly in front of the 
wheels, the stones loosened by the horses' feet would be rolled down 
by the wheels of the wagon. This is a matter of some moment with 
broken-stone roads, but is not important with earth roads. How- 
ever, a few teamsters using earth roads hitch their horses in front of 
the wheel, to enable their horses and wheels to run in the beaten 
track made by the feet of preceding horses not hitched in front of 
the wheel. 

205. CARE OF THE SURFACE. The most important work in 
maintaining an earth road is to keep the surface smooth so that the 
rain water will flow quickly into the side ditches. If the surface of 
an earth road is properly formed and kept smooth, the water will be 
shed into the side ditches and do comparatively httle harm; but if it 
remains upon the surface, it will be absorbed and convert the road 
into mud. 

There are three classes of machines in use for filHng ruts and 
depressions and in keeping the surface smooth. They are the road 
drag, the scraping grader, and the V road-leveler. 

206. Road Drag. The road drag is the simplest, the cheapest, 
and the most effective implement for smoothing the surface of a 
road. Four type forms of the road drag are shown in Fig. 30, 31, 
32, and 33, pages 118 and 119. Each consists essentially of one or 
more cutting edges which stand obliquely across the road as the 
implement is drawn along the road. The road drag is designed to do 



118 



EAKTH ROADS 



[chap. Ill 



three things, viz., (1) smooth the surface by paring off the high 
places and filling up the low spots; (2) move a Httle earth toward the 
center of the road to compensate for the wash of the water in reducing 
the crown; and (3) puddle or harden the surface by dragging it 
when wet. To accomplish the first purpose, the cutting edge must 
make a considerable angle with the line of draft, so that the earth 
that is pared from the high places will drift along in front of the cut- 
ting edge and fill up the low spots. To secure the second object, 
the front end of the cutting edge should be toward the outside of 
the traveled way, so the drifted earth will be moved toward the center 
of the trackway. To accompHsh the third purpose, the road should 
be dragged when it is wet. Working the soil when it is wet, puddles 
it; when it dries, it will be hard and more nearly waterproof. Under 
favorable conditions each successive dragging adds a thin* layer of 
tough and impervious material; and consequently the frequent 
dragging of an earth road builds up a crust that does not easily become 
muddy. 

The shcker, or lapped-plank drag, Fig. 30, is easily and cheaply 
made; and is to be preferred when the road is quite soft, and also in 
soil that is too sticky to flow along the blade of the other forms of 
drags. In these cases the shcker smooths the road partly by com- 




FiG. 31. — Split-Log Road Drag. 



Fig. 32. — Plank Road Drag. 



pressing the high places and partly by cutting them off, and thus 
fills up the low places and gives the water an opportunity to run off. 



ART. 2] 



MAINTENANCE 



119 



The split-log drag, Fig. 31, is commendable chiefly because of the 
ease with which it can be made when a suitable log is at hand. The 
log should be 7 or 8 feet long, and 10 or 12 inches in diameter. The 
braces between the two halves of the log may be roughly hewn and 
the ends be made to fit into 2-inch auger holes in the slabs. The 
braces should be long enough to hold the two slabs about 30 inches 
apart. The braces should be fastened in place by driving wedges 




L 


i... ^M" 


^ 





Fig. 33, — Adjustable Three-Bladei Steel 
Road Drag. 



Fig. 34. — Road Sucker at Work. 




Fig. 35. — Work of Road Slicker. 



Fig. 36. — Split-Log Drag at Work. 



into their outer ends. Fig. 36 shows a crude split-log with removable 
platform doing excellent work. 

The dimensions and construction of the plank drag are shown 
in Fig. 32. If the main planks are hard wood and 2^ or 3 inches thick, 
the reinforcing planks may be omitted. 

Fig. 33 shows an adjustable steel road drag. The cutting blades 
can be tilted forward or backward by the hand lever. Similar steel 
drags are made with two blades. Non-adjustable 2-blade and 
3-blade steel road drags also are upon the market. 



120 EARTH ROADS fcHAP. Ill 



207. Rules for Using Road Drag. The following rules should 
be observed in dragging earth roads: 

1. Remove all loose stones from the road before dragging it. 

2. The depth of cutting may be regulated by the length of the 
hitch chain. A short chain causes an uplift, and hence a lighter cut; 
and vice versa, a long hitch causes less uplift, and hence a deeper 
cut. The depth of cut can also be varied by the driver moving 
forward or backward on the drag, or e\en by inclining his body. 

3. The driver should stand upon the drag, and be ready to shift 
his position as the circumstances demand. However, if an unusually 
soft portion of the road is encountered, it may be best for the driver 
to walk. 

4. Drive the team in a walk. 

5. Drive a horse on each side of the right-hand wheel track, with 
the front end of the cutting edge on the outside of the traveled way, 
and proceed to the end of the portion of the road to be dragged; and 
then on the return do similarly for the other wheel track. Of course, 
if the traveled way is wide, it may be necessary to make more than 
one round trip. 

6. The best time to use the drag is when the road is drying out, 
while the soil cuts easily, and is damp or wet enough to puddle ; but the 
soil should not be so sticky as to cling to the cutting edges of the drag. 

7. Do not move too much earth toward the center of the road. 
There are two reasons for this rule. First, it is important to keep 
the road surface as hard as possible, and hence no more earth should 
be loosened than just enough to make the surface smooth. An excess 
of loose earth will make the road dusty in dry weather and muddy 
in wet weather. Second, only enough earth should be moved toward 
the center to counteract the effect of the rain in reducing the crown. 
An excess crown will concentrate travel at the center and cause deep 
ruts to form, which will hold water and make mud. If the crown 
becomes too high, drag it once or twice in such a way as to work 
the soil away from the center. 

8. By hitching the team close to the front end of the drag, the 
blade will cut like a plow ; and the machine can then be used to remove 
weeds or deepen the side ditch. With this hitch, the driver should 
stand near the forward end of the blade, and should throw his 
weight forward or backward as the work may require. Care must 
be taken that the entire drag is not tipped over forward. When 
weeds clog the cutting edge, they can be removed by the driver's 
shifting his weight to the rear end of the cutting edge. 



ART. 2] MAINTENANCE 121 



9. The road should be dragged after it has been roughened by 
being used when muddy; but the dragging should not be postponed 
until the soil has ceased to be mellow and easily moved. It is a 
waste of time to postpone the dragging until the road has become 
dry and hard. 

10. The most effective time to drag a road is in the spring imme- 
diately after the frost is out. 

11. If the roadway is very rough and contains many deep ruts and 
holes, it may be best to drag it when it is quite slushy. In this case 
a lapped-plank smoother, or slicker, is better than the split-log, 
plank, or steel drag. The hitch to the slicker should be such that the 
outer end of the machine is a Httle ahead, so as to fill up the holes 
and ruts. 

12. If a slushy road is dragged or smoothed just before freezing 
weather, the surface will freeze and make a fine, smooth, hard road. 

208. Cost of Dragging. The cost of dragging the road depends 
somewhat upon the condition of the road and also upon the demand 
for men and teams for agricultural work; but usually the cost per 
mile per round trip of an 8-foot drag will be about 50 to 60 cents. 
See § 229 for further details. 

209. Scraping Grader. This machine is described in § 155-56, 
and its use in road construction is explained in § 157-60. It is pro- 
posed here to consider the use of this machine in the maintenance 
of a road. 

If the road drag (§ 206) were frequently and efficiently used, the 
road would be kept in a fairly good condition; but for one reason 
or another, the roads are not usually dragged when the work can be 
done most efficiently, and consequently are allowed to dry out 
rough and full of ruts. After they have reached this stage, it is 
nearly or quite impossible to secure a smooth surface with any form 
of road drag. Under these conditions the surface can be restored by 
running a scraping grader over the road so as to plane off the ridges 
and fill up the ruts. 

210. Operating the Scraping Grader. Commence at the ditch and 
work toward the center, scraping with the entire length of the blade. 
The blade should stand nearly square across the road, and consider- 
able earth should be shoved along in front, — enough to fill the depres- 
sions ; — but only enough earth should be moved toward the center of 
the roadway to replace that washed down by the rains. The sur- 
plus earth should be uniformly distributed over the surface, by 
carrying the rear end of the blade a httle higher than the point. A 



122 EARTH ROADS [CHAP. Ill 

ridge of earth should not be left in the center of the road, since it 
will but slowly consolidate and is hkely to be washed into the side 
ditches to make trouble there. 

This work should be done early — before the ground becomes 
hard and difficult to work, before traffic has been compelled par- 
tially to do the work of the road leveler, and while the surface is in 
condition to unite with the loose earth left by the machine, and 
when the roots of grass and weeds do not interfere with the work of the 
blade. Unfortunately this work is often postponed until the ground 
is so hard that it is impossible to do a thoroughly good job. If 
the ground is a little too wet for tillage, it is all the better for road 
making, since it will pack and harden better than though it were 
drier. After the ground becomes dry and hard, it is not only more 
laborious and expensive to secure a smooth surface; but the newly 
repaired road may for weeks be in a worse condition than before 
it was worked, since the loose earth is too dry to pack under traffic. 

211. A common error in scraping roads is not to begin far enough 
down in the ditch, thus leaving a shoulder which prevents the water 
from flowing from the roadway into the side ditch. Fig. 37 shows a 



Fig. 37.^ — Objectionable Shouldeks Left' by Scraping Grader. 

road finished in this way. The shoulders not only dam back the 
water, but also narrow the roadway; and after weeds and grass have 
got a good start, it is improbable that the shoulder will be cut off 
next time the road is scraped, and in all probability each successive 
scraping will make a bad matter worse. However, with a skilful 
use of the scraping grader these shoulders can be cut off. 

Not infrequently writers claim that material from the side 
ditches should not be placed upon the roadway. Unquestionably 
silt from the bottom of the ditches is undesirable material with 
which to built or repair a road; but in ditches properly constructed 
and cared for, there is not much, if any, of such materiel, and if any 
of it is removed with the scraping grader it is so thoroughly mixed 
with good material before it reaches the roadway as to be practi- 
cally harmless. The advice against fine material from the side 
ditches originated when the drag scraper was the chief tool used in 
repairing roads, and the advice has unfortunately outlasted its 
usefulness. 



ART. 2] 



Maintenance 



123 



212. Cost with Scraping Grader. The scraping grader may be 
drawn by three 2-horse teams or by a traction engine; but unless 
the roads are very hard and tough, horses are more economical than 
the tractor, since the grader is too small to be used economically with 
the ordinary tractor. 

To shape up the road in the spring, six horses and three men are 
required to operate the scraper. The wages of a team and driver 
will usually be $3.00 or $3.50 per day, since generally the scraping 
should be done when farmers are busy with farm work, and since 
the work is hard on teams. The cost of operating the grader is then 
$9.00 to $10.50 per day. A scraper will on the average smooth up 
3 or 4 miles per day, at an expense of $3.00 to $3.50 per mile, or, in 
round numbers, including repairs and loss by bad weather, say, 
$4.00 per mile. If the road is not very rough, two rounds are 
enough; and if it is very bad four may be required, but usually three 
rounds are sufficient. If the work is postponed too long, the cost may 
be nearly double the above. 

The cost of smoothing up city streets would be considerably 
more than the above, because of the time consumed in passing side- 
walk crossings or in turning to avoid them. Particularly under such 
conditions, the amount of work accomplished in a day depends greatly 
upon the training of men and horses. 

213. The V Road-Leveler. One form of this machine is shown 
in Fig. 38. It consists of two cutting blades 18 or 25 feet long, 
suspended from a platform which 
carries the operating machinery. 
The spread of the cutting blades 
and also the relative height of 
the two ends are adjustable. 
The machine is drawn behind a 
15 to 25 H.P. tractor. With the 
longer blades the leveler will 
smooth up a maximum width of 
30 feet at one time; and with 
the shorter blades 22 feet. 
Either size machine can shape 
up a roadway 10 or 12 feet 

wide. There are at least two other somewhat similar forms of this 
machine. 

The scraping grader is too large for a convenient number of horses, 
and too small for a tractor; and hence the V road-leveler was 




Fig. 38. — The V Road-Leveler. 



124 EARTH ROADS [CHAP. Ill 

invented to economically utilize the full power of an ordinary trac- 
tion engine. 

Sometimes three large adjustable steel road drags are hitched 
behind a traction engine, and do substantially the same work as a 
V road-leveler. 

Sometimes a drag or a roller is hitched behind the V road-leveler, 
to level down or consoUdate the loose earth left between the cutting 
blades. 

214. Filling Holes. . After the road has been smoothed by the 
scraping grader or the V road-leveler, it is a good plan, particularly 
if the road is very rough, to send a man with a shovel to fill up all 
ruts and depressions that were too deep to be filled by the scraper. 
If a deep hole has been filled by the scraper, it is well to add a little 
more earth to provide for settlement in order to prevent the re- 
appearance of the hole. The new material should be trodden or 
tamped solidly into place. 

Holes and ruts in an earth road should never be filled with stone, 
brick, or coarse gravel. The hard material does not wear uniformly 
with the rest of the road, but produces bumps and ridges, and 
usually results in making two holes, each larger than the original 
one. It is a bad practice to cut a gutter from a hole to drain it to 
the side of the road. FilUng the hole is the proper course, whether 
it is dry or contains mud. 

215. Removing Stones. All loose stones larger than 2 inches 
in diameter should be removed; and stones projecting above the 
surface should be dug out. They should be taken entirely away, 
or be piled beyond the side ditches; and should never be left just 
outside of the trackway, as is sometimes done, where they restrict 
traffic and obstruct the flow of water from the center of the side 
ditches. 

216. Care of Side Ditches. The side ditches should be ex- 
amined in the fall to see that they are free from dead weeds arid 
grass; and late in the winter they should be examined again to see 
that they are not clogged with corn stalks, brush, etc., washed in 
from the fields. The mouth of culverts should also be cleared of 
rubbish, and the outlet of tile drains should be opened. Attention 
to side ditches will prevent overflow and washing of the road-bed, 
and will also prevent the formation of ponds at the roadside and 
the consequent saturation of the road-bed. The road care-taker 
should frequently go over his portion of the road just as a heavy 
fall of snow is going off, for it is then that water does most damage. 



ART. 2] MAINTENANCE 125 

217. Care of Roadside. It is desirable that the roadside 
should be so cared for as to secure a coating of grass instead of un- 
sightly and noxious weeds. This can usually be accomphshed at a 
slight expense by an occasional mowing. 

218. Care of Trees and Hedges. Earth roads should have 
plenty of hght and air. Trees along the road may add beauty to 
the landscape (§ 195), but shade is nearly sure to breed mud holes. 
In some localities and under some conditions, shade upon the road 
surface should be eliminated by cutting down the trees or by trim- 
ming them so as not to keep the breeze and sunlight from the road; 
but in other locaHties and under other conditions, a little of the utihty 
of the road may be sacrificed to secure attractiveness in the general 
surroundings. 

A tall hedge cuts off the view of the adjacent country, shuts out 
the breeze, in a dry time keeps in the dust, and in a wet time retards 
the drying of the road. The hedges usually belong to the adjacent 
private property, but in most states the height is limited by statute; 
and in such cases the road officials should enforce the law. If there 
is no law governing hedges and trees near the road on private 
property, the road officials should use all possible diplomacy to have 
trees and hedges trimmed with reference to the benefits of the road. 
In this connection, see § 219. 

219. Obstruction by Snow. In locaHties subject to heavy 
falls of snow, it is an important matter to keep the roads from be- 
coming obstructed by it during the winter. In some countries where 
there is only an occasional fall of snow, as in France, it is customary 
to remove it from the surface of the road; but where there is much 
snow, it is only necessary to compact it so as to make the road pass- 
able. This is done by driving horses or cattle back and forth along 
the road, or by rolling the road with a heavy farm-roller. The use 
of the roller should commence with the first storm of the season and 
be continued as often as necessary through the winter. In the case 
of a very heavy storm, the roller should be sent over the roads at 
intervals during its continuance. Obviously this work must be 
done by the residents along the road. 

Snow and ice frequently accumulate in the side ditches to such a 
height as to make the surface of the road the principal line of drain- 
age. In the spring, when this occurs on earth roads, a large volume 
of snow-water flows down the road, and often seriously damages it 
by washing gulhes in the surface. The best water-bound macadam 
roads may be seriously injured in this way; and in some localities 



126 EARTH ROADS [CHAP. Ill 

it is necessary to remove the snow from the side ditches to prevent 
damage of this character. The difficulty and expense of keeping 
the side ditches free from snow and ice is greatly increased if the 
ditches are deep and narrow, particularly since with this form of 
ditch it is necessary to maintain a culvert or covered gutter at the 
junction of cross roads and private drives with the main highway. 
These culverts are very liable to become clogged with icy snow, and 
it is nearly impossible to clear them without digging them up — 
which is rarely practicable. This difficulty could be obviated, or 
at least greatly decreased, by constructing shallow side ditches; 
and, if necessary, laying a large tile drain under the ditch to carry 
the surface water. 

The cost of work occasioned by snow can be decreased by proper 
attention to the fences, underbrush, etc., along the side of the road. 
Snow drifts are caused by the obstruction of the currents of air near 
the ground — those that carry the drifting snow. In forests the winds 
do not have sufficient velocity to carry the snow, and consequently 
it lies evenly and of a uniform depth; but in the open country 
it drifts with the wind. Fences and shrubbery which retard the 
winds but permit the snow to blow through, cause the snow to pile 
up on the sheltered side and possibly to block the road and ditches. 
The fences should be either quite open or very close. A high tight 
fence obstructs the wind, and causes the snow to pile up on the wind- 
ward side. If the roadside is partially obstructed, the wind moves 
the loose snow into earth cuts and also into the beaten snow path, 
and fills them up. Filling the snow trackway gradually raises the 
traveled portion of the road until turning out into the loose snow 
becomes dangerous. 

220. In Vermont, '' in many townships the cost of keeping the 
roads passable in the winter is one third, and in some one half, of 
the total amount expended on the highways, and the average for 
the state is one eighth," or $4.30 per mile per annum. 

221. The possible cost of maintenance on account of snow should 
be considered in locating a road (§ 100-02). 

222. Systems of Maintenance. The administration of the 
maintenance of earth roads is a matter of great difficulty. The 
difficulties are: 1. The justifiable expense is comparatively small; 
and hence the man who does the work must have charge of a consider- 
able mileage, and consequently can get over the road only at infre- 
quent intervals. 2. In many states the maintenance is done in 
whole or part by the labor tax, which at best is inefficient. 3. The 



ART. 2] MAINTENANCE 127 

amount of work required may vary suddenly and greatly with local 
storms. 4. The administration is usually in the hands of an inexpert 
man or board to whom the care of the roads is only an incident in 
private or official duties. In this connection, see § 41. 

As a rule inadequate attention has been given in this country 
to the maintenance of roads, and this is particularly true of earth 
roads. For the latter there have been only a few attempts to develop 
an efficient system, and even they are still in the experimental stage. 
Further, the conditions vary so greatly in different parts of the 
country that a system that is reasonably successful in one locality 
may be wholly inapplicable in another. 

The various systems that have been attempted may be classified 
somewhat roughly as follows: (1) intermittent repairs; (2) continu- 
ous repairs; (3) continuous maintenance; and (4) contract system. 
These systems differ greatly and over-lap as applied in different 
localities. 

223. Intermittent Repairs. This system is with propriety often 
called the pathmaster system. In this system the care of the roads 
is left to the official pathmaster, who has charge of 8 or 10 miles of 
roads, and who superintends the working out of the labor road-tax. 
This is the most common but least efficient system. This system 
has all the objections enumerated in § 222. 

In practice this system is a method of intermittent repairs rather 
than maintenance, that is, under this system the roads are allowed 
to get into a comparatively bad condition before they are repaired 
or restored. 

224. Continuous Repairs. This system consists in putting 
the care of the roads of a township or its corresponding administrative 
road-unit into the hands of a small squad of men who give all or 
substantially all of their time to the care of the roads. These men 
are provided with a scraping grader (§155) or a V road leveler 
(§ 213), and teams or a traction engine, shovels, picks, etc. 

The theory of this system is that the roads, or at least the main 
ones, will not get very bad, or be bad very long, before the repair 
gang will be along. The advantages of this system are : (1) the squad 
is employed continuously, and hence becomes more expert; and (2) 
the amount of road cared for is so great as to warrant providing the 
squad with a good outfit. The disadvantages are: (1) the work is 
not done at the most advantageous time, i. e., when the soil is most 
easily worked; and (2) the roads are not in good condition all the 
time. 



128 EARTH ROADS [CHAP. Ill 

• 

225. Continuous Maintenance. The essential feature of this 
system is that the care of a definite road is allotted to one man, who 
makes this his first business. The system is sometimes called the 
patrol system, and takes this name from the method long employed, 
chiefly in Europe, in caring for water-bound macadam roads in which 
a man devoted all of his time to patrolling and caring for a compara- 
tively short piece of road. 

It is not usual to attempt formally to maintain any but the most 
traveled earth roads. Even on these roads the amount of work 
required varies so much with the season and with th.3 frequency 
of storms, that the section must be comparatively short; and there- 
fore at times there is not work enough to require the full time of the 
patrol. To meet this condition it is customary to employ a man who 
lives near the road, to labor upon the road when directed. The 
direction of the patrols is in the hands of a township official or 
foreman; and a general supervision of all the foremen is in the hands 
of the county engineer. 

The only work ordinarily attempted is to drag the road as needed. 
The overseer or superintendent communicates with the patrols by 
telephone, both to inquire as to the condition of the roads and 
to order work done. The patrol is usually required to report by 
postal card as to the work done and the time required. In some cases 
a report is required for each day's work, but sometimes only a weekly 
report is demanded. In some states a portion of the road tax is set 
apart by statute to pay for dragging, and can not be used for any other 
purpose. 

The length of the sections vary with the possibility of securing 
competent patrols; but are preferably not more than a mile or two 
each, so as not to interfere too much with the other duties of the 
patrol. 

Prizes are sometimes given for the best work, the money for the 
same in some cases being taken from the road taxes and in other cases 
is contributed by Chambers of Commerce, etc. 

By this system of maintenance the roads are kept all the time 
in a fairly good condition. In a number of cases where tried the con- 
clusion reached was that the condition of the roads was much better 
under this than under other systems, and at the same time the total 
cost was less.* 

226. In those states in which an attempt is made to continuously 

•For one example, see Engineering Record, Vol. 73 (1916), p. 643-44; and for another' 
see Engineering and Contracting, Vol. 38 (1912), p. 714. 



ART. 2] MAINTENANCE 129 

maintain the earth roads, there is usually a law prohibiting the use 
of the dragged surface until it has dried out so that a wheel will not 
make a rut. 

227. Maintenance by Contract. In view of the ordinarily 
inefficient system of caring for roads, it has frequently been pro- 
posed to maintain them by contract. As a rule, work done under 
the supervision of a contractor who has pecuniary interest in the 
result is more economical than that performed under the direction 
of a pubhc official; but it is not wise to do work by contract unless 
the amount required can be approximately known beforehand, and 
also unless the character of the performance can be easily deter- 
mined after completion. Neither of these important conditions 
would be present in a contract for the maintenance of a public high- 
way. Owing to the indefiniteness as to the amount and character 
of the work to be done, it is not at all certain that the maintenance 
could be provided for by contract for a sum less than the public 
officials could do the work under the present system. The inspec- 
tion would finally depend upon the road official, and the letting of a 
contract would increase the difficulties and expense of supervision. 

It is claimed that the contractor could maintain a trained corps, 
and therefore do better work than can be done by the present system; 
but it is doubtful if contract work would be any cheaper or better 
than the method described in § 225. 

228. EXPENDITURES FOR MAINTENANCE. There are but few 
data concerning cost of maintaining earth roads, and much of that 
is very indefinite since the conditions of soil, weather, etc., are not 
stated and also since no definite information can be stated as to the 
quality of the maintenance. 

229. Dragging. The cost of systematically dragging a road in 
Arkansas was $11 per mile per annum, or 50 cents for each dragging.* 

In Tennessee 30 miles of roads in sections of 3 miles each were 
dragged during the months of December, January, February;, and 
March, under the continuous maintenance system. The price for a 
man and a 2-horse team was 30 cents per hour. The county furnished 
the drags. Prizes were offered for the best kept road, and the prize 
was awarded to a road for which the cost was $5.00 per mile per 
annum. 

In Hale Township, Carroll County, Missouri, an overseer is in 
charge of every 8 miles of road, and has ten patrols, each in charge 
of a section. After each rain the overseer by telephone calls upon the 

* Bui. No. 48 of the U. S. Office of Public Roads, p. 46-7. 



130 EARTH ROADS [CHAP. Ill 



patrols to drag the roads. The cost of maintaining the roads dur- 
ing April, May and June is from $10 to $15 per mile, including $15 
for each overseer. 

Clayton County, Iowa, from 1913 to 1916 maintained the county 
roads, i. e., 226 of the 1350 miles in the county, by the continuous 
maintenance system. The patrol section was from 7 to 10 miles. 
Some of the patrohnen put in all their time, but some only part 
time. The patrolmen hired help as was necessary. Each patrolman 
furnished his own team and wagon. Usually three horses were used 
on a drag. The average pay was 27i cents per hour for patrolmen, 
47^ cents per hour for man and team, and 10 cents per hour for each 
extra horse. Patrolmen's assistants were paid 25 cents per hour, and 
45 cents per hour for man and team. The average cost of dragging 
was 56j cents per mile for one round trip. The total cost for main- 
tenance and repairs averaged about $56 per mile per year. The 
average cost of dragging in Clayton County was 56J cents per mile 
per round trip; while that in other counties of the state was 71.3 
cents per mile per round trip.* 

230. Total Cost of Maintenance. The following data are for 
the maintenance of 70 miles of road during the years 1909 and 1910 
in northern Michigan, f The roads were maintained by the patrol 
system under the direction of the County Engineer. The roads 
were '' floated," i. e., dragged with the slicker or lapped-plank 
drag, once when the frost was partly out and once after it was com- 
pletely out. The roads were dragged after every heavy or protracted 
rain during the season. After the roads had settled in the spring, 
every hole was filled, and the roads otherwise put into good condition. 
The patrols were required to be on the road and work upon either 
the road-bed or the drainage system, two specified days in each month. 
They were expected to mow weeds and brush on the roadsides, break 
through the snow in winter, and keep the road to the standard of a 
good earth road. The cost was as shown in the tabular statement 
on the opposite page. 

'' The greater cost of dragging in 1909 was because the roads 
had not previously been dragged; and the greater cost of general 
repairs in 1910 was because of the higher standard of maintenance." | 

231. Table 20, page 132, gives the results of a test in maintenance 



* Engineering Record, Vol. 73 (1916), p. 643. 

t K. I. Sawyer, in Proc. 1915 Short Course in Highway Engineering, University of Michigan, 
p. 62-64. 

X Private letter from Mr. Sawyer, 



ART. 2] MAINTENANCE 131 

conducted by the U. S. Office of Public Roads.* '' Before the main- 
tenance was undertaken the county repaired the road and put it in 
good shape. The repairs consisted in shaping parts of the road with 
a scraping grader, clearing and widening the ditches and clearing 
the culverts, and applying gravel to a section of the road. The cost 

1909 1910 

Length maintained, miles 70 . 5 72 . 5 

Length of patrol section, miles ■. . . 6 4-6 

Average cost, per mile : 

Dragging $26.17 $8.65 

Patching surface, culvert and ditch work, cutting 

weeds and brush 8 . 56 19 . 77 



Total cost per mile $34.73 $28.42 

Cost of dragging one mile one time . 925 

of the repairs was $700. On the 8 miles of road there are 4 bridges, 
19 culverts, 54 drain pipes under driveways, 59 intersecting roads 
with drain pipes, 42 intersecting roads without drain pipes, and 10 
small wooden bridges across the gutter. The entire 8 miles of road 
is well traveled, and there is considerable heavy teaming over parts 
of it A portion of the road is also used by United States cavalry. 
There is also considerable automobile traffic on some portions. 
A travel census for 3 days in March on one section of the road shows 
the following : Loaded 1-horse wagons, 15; unloaded 1 -horse wagons, 
58; loaded 2-horse wagons, 38; unloaded 2-horse vvagons, 49; loaded 
4-horse wagons, 9; unloaded 4-horse wagons, 4; saddle horses, 96; 
and motor runabouts, 1. The patrolman furnished a horse, cart, 
and small tools. He was supplied with a plank road-drag, and re- 
quired to furnish two horses to drag the road whenever it was in 
suitable condition for dragging, usually following each rain. He 
was paid $60 per month and $1.00 per day extra whenever he 
used two horses to drag the road. His presence was required on 
the road from 8 a.m. to 4:30 p.m., with thirty minutes allowed for 
lunch." 

" The cost of dragging was approximately $1.25 per mile for each 
dragging of three round trips. The item of $169.88 for repairing, 
clearing and improving ditches and underdrains was large, because 
it was found necessary as the year progressed to rebuild entirely 
portions of the gutters and ditches. 

* Engineering and Contracting. Vol. 38 (1912), p. 714. 



132 



EARTH ROADS 



[chap. Ill 



TABLE 20 
Cost of Maintenance of 8 Miles of Road in Alexandria County, Virginia, 

From December 17, 1911, to June 30, 1912 



Ref. 

No. 



Kind of Work. 



Days. 



Total. Per Cent. 



Cost. 



Total. Per Mile. 



Dragging 

Repairing, cleaning and improving 

ditches and xinderdrains 

Cutting brush, etc 

Picking off stones 

Taking census 

Inspection during storms 

Clearing fallen trees, building 

guard rails, etc 

Total for 6.5 months 



38.5 

73. 
26.5 
10.5 
10. 
5.5 

6. 



22.7 

42.9 

15.6 

6.2 

5.9 

3.2 

3.5 



$128.89 

169.88 
61.78 
24.55 
23.36 
12.67 

13.86 



$16.11 



21 
7, 
3. 
2. 
1. 



1.73 



170.00 



100.0 



$434.99 



$54.34 



" The following conclusions are clearly demonstrated by the 
experiment: (1) The use of the drag has greatly improved the 
daily condition of the road and rendered it smooth and comfortable 
for travel for a greatly increased number of days in bad weather. 
(2) A width of earth road in excess of 24 feet is unnecessarily expensive 
to maintain. (3) The presence of the patrolman during storms and 
immediately after, saves considerable expense for repairs due to the 
wash of surface water. (4) The existence of poorly drained private 
driveways and intersecting roads is a constant expense for main- 
tenance. (5) The use of small tiles for side drains and the building 
of wooden bridges over gutters at driveways is a serious obstacle 
to proper drainage. The pipe is usually laid at insufficient depth, 
and becomes broken and clogged. It would appear that paved gut- 
ters at driveways would not be unduly expensive in the long run, and 
would certainly provide better surface drainage. (6) It is not 
economical to employ a patrolman during the winter months, unless 
his time can be used to advantage in clearing brush and rubbish from 
the right-of-way; but a man should be constantly in charge of every 
mile of road to inspect it during storms, and to free the ditches. 
(7) The presence of old cobble stones and poorly consoHdated 
coarse gravel is a serious impediment to the use of the drag. The 
stones must be removed from the road before dragging can be suc- 
cessful. (8) There is ample work for one man continuously during 
8 or 9 months of the year; and there is difficulty in combining road- 
patrol work with the dragging of earth roads." 



ART. 3] SURFACE OILING 133 

232. Table 21 gives details of the average annual expenses for 
roads in Champaign County, Ilhnois. Notice that part of the 
expenditures are for maintenance proper, while part are for im- 
provements in the original construction. 

TABLE 21 
Average Expenditures per Mile of Earth Roads in Champaign Co., 111. 

1. New steel bridges — exclusive of county aid * $16 . 20 

2. Drainage 6.32 

3. THe culverts 1 .32 

4. Repairs of bridges and culverts 2 . 93 

5. Grading (not simply smoothing and leveling) 1 . 43 

6. Smoothing and leveling (not grading) 2 . 83 

7. Mowing the roadsides 1 . 14 

8. Administration 2 . 69 

Total average annual expenditure $34 . 86 

It is not known that any data similar to those in Table 21 were 
ever before collected, and hence there is no means of knowing 
whether these data are representative. These expenditures were 
in 1900 before the use of oil in maintaining earth roads (see Art. 
3 of this chapter). It is probable that the expenditure for bridges 
is considerably larger than the average. Champaign County is 
rolling prairie situated in the corn belt. There are no large streams, 
and practically all the land is under cultivation. Farm lands with- 
out buildings then sold at $80 to $100 per acre. There are 1.97 
miles of road per square mile of area outside of cities and villages. 
All the roads have a black loam surface. 

Art. 3. Surface Oiling 

233. The surface of an earth road is sometimes treated with oil 
to prevent dust and also to aid in keeping the surface smooth. In 
small towns and villages the former is the chief purpose; while on 
rural roads the latter is the main, or sole, object. 

234. Preventing Dust. The annoyance from dust usually 
reaches its maximum in small towns and villages, owing to the 
concentrated travel and the presence of more people to be incon- 
venienced. The dust can be greatly reduced by properly dragging 
the road. The surface should never be dragged when dry, since the 

* In Illinois the county pays half the expenses of bridges costing more than a specified per 
cent of the assessed value of the township. The expenditures by the county for new steel 
bridges is nearly as much as by the township. 



134 EARTH ROADS [CHAP. Ill 

resulting loose earth will speedily be ground into dust; and for the 
same reason, an excess of loose earth should not be left in the center 
of the road. 

Within the last decade many dust palliatives and preventatives 
have been used; but oil is the agent most frequently employed on 
earth roads. Crude tar has been employed as a dust palliative; 
but on account of its injury to rubber tires and also on account of 
its tracking into houses, it is not satisfactory. 

235. Effect of Oil on Maintenance. Loam and clay roads 
are improved by a little moisture — just enough to keep them damp 
and dark without making them soft or spongy. In dry cKmates the 
roads not only become excessively dusty, which is a great discom- 
fort, but also wear into pot-holes, which are dangerous, since being 
filled level-full of dust their presence is not revealed until a wheel or 
a horse's foot plunges into them. In some localities the dust at 
times is practically hub deep, and is not only an annoyance but 
greatly increases the tractive resistance. In arid climates and even 
in dry times in humid climates, sprinkUng with water is an effective 
means of maintenance. A layer of straw is sometimes put upon the 
road to subdue or prevent the dust; but of course the effect is only 
temporary. 

Recently crude petroleum has been employed on highways, 
instead of water, to prevent dust. Oil has been used for this purpose 
in Southern California more than elsewhere, primarily on account 
of the high grade of oil that is available at low cost, hut also on 
account of the sandy soil, the semi-arid climate, and the absence 
of freezing weather. 

Oil when appHed to loam and clay roads, reduces the dust, makes 
the road-bed at least partially non-absorbent, and gives a dark- 
colored surface which is more pleasing to the eye than the ordinary 
Hght, dusty soil. Since the road-bed is less absorbent, it is not so 
easily worked into mud; and besides the oily surface more readily 
sheds the rain water into the side ditches. In localities where there 
is frequent thawing and freezing and also much rain, the effect of 
oil on loam and clay roads does not last through the succeeding 
winter, except in case of an unusually dry winter and spring. In 
comparatively dry climates and upon a sandy soil, the continued 
application of suitable oil to the surface tends to gradually improve 
the condition of the road-bed. However, whatever the character 
of the soil, roads having a considerable hauling are not materiall}^ 
improved either temporarily or permanently. 



ART. 3] SURFACE OILING 135 

236. Preparing the Surface. The surface should be smooth 
and properly crowned, so as to shed water into the side ditches. 
The surface can be properly prepared with a road drag (§ 206) or 
a scraping grader (§ 155), according to the degree of roughness and 
the dryness of the soil. If much earth is moved in shaping the sur- 
face, the road should be subjected to travel to consoHdate the loose 
earth; and if depressions appear these should be filled, and be con- 
soUdated by travel or other means before the oil is applied. The 
expense incurred in securing a hard, smooth, properly crowned sur- 
face will more than be made up by the increased effectiveness of the 
oil treatment. For the best results the upper 2 inches of the road 
should be fairly dry; but the surface should be free from dust. 

237. The Oil. For a discussion of the origin and character 
of road oils, the method of shipping them, and specifications for oils 
suitable for the different kinds of soil, see Art. 2 of Chapter VIII. 

238. Applying the Oil. The oil should be applied at the rate 
of one fourth to one half gallon per square yard of surface. If the 
road has never been oiled, or if more than one season has elapsed 
since a previous oiling, about a half gallon per square yard will be 
required. If the road has been oiled earUer in the season, one 
fourth to one third of a gallon per square yard will usually be 
satisfactory. It is much better to apply a small amount of 
oil twice each season rather than to put on the full quantity 
in one apphcation. When too much oil is applied, it is not only 
wasted, but is often disagreeable to the users of the road. The 
first time the road is oiled, the best results may be secured by using 
a thin product that will penetrate the road-bed to a considerable 
distance and at the same time contain as much binding material as 
possible. The oil should be thin at ordinary atmospheric tem- 
peratures, and applied cold. If a thick oil is used for the first 
apphcation, it will not penetrate to any considerable distance, but 
will form a mat upon the surface; and consequently, if the road is 
not well underdrained, the accumulation of moisture under the mat 
may cause the road to dry out more slowly, and may also cause the 
mat to break up. After the top layer of the road has been satu- 
rated, a heavier oil may then be used; and it is best applied when 
hot. 

239. The uniform distribution of the oil is one of the essential 
requirements for success. An ordinary street sprinkler or a home- 
made device attached to a thresher tank-wagon may be utilized 
for distributing the oil, although considerable care is required to 



136 EARTH ROADS [CHAP. Ill 

secure the right amount and a uniform distribution. Much better 
results can be secured by the use of specially designed pressure dis- 
tributor tank wagons or trucks. There are a number of such wagons 
and trucks on the market. Some of them are equippad with a heat- 
ing device so that hot oil may be applied when required; and all 
have pumps for distributing the oil uniformly and under pressure, 
and some have a device for spraying the oil upon the road. 

On earth roads the use of the pressure distributor is useful mainly 
to secure the proper quantity; but on a gravel or broken-stone road 
the pressure distributor is important, since applying the oil with 
force blows the dust off the pebbles or stones and permits a better 
adhesion of the oil. The chief advantage of the spray is that it 
secures a more uniform distribution. 

The distributor should be so regulated that the width to be oiled 
will be covered by one or more uniform strips without any over- 
lapping. Any spots between the strips that are not covered by the 
machine distributor, should be covered with a hand-pouring can 
follov/ing immediately after the distributor. For the best results 
the oil should be applied in two equal coats with an interval of at 
least 5 or 6 hours between them to allow the first to be absorbed 
before the second is appUed. Travel should be barred from the road 
for 3 days after the first coat is appUed, to allow the oil to be absorbed. 

Fig. 39 shows a pressure tank wagon for distributing road oil. 
This road oiling-machine is provided with an oil-burning heater and 
a jacket around the tank; and also has two pumps for applying 
the oil under pressure and regulating the amount. Fig. 40 shows 
another form of road oiler. 

240. Cost of Oiling. The cost of preparing an earth road 
for oiling will vary greatly, depending upon the condition of the 
surface. If the surface is not already well crowned, the road 
should be treated with either the road drag or the scraping grader. 
However, such work should not be considered as part of the cost 
of oiling; but should be considered as part of the cost of construc- 
tion or of maintenance, since the road should be properly crowned 
and be kept so whether or not it is oiled. Even though the sur- 
face is properly maintained, it will probably be necessary to drag 
the road and otherwise shape it up; and this cost may be $10 to 
$25 per mile. 

The price of oil for earth roads varies from 4 to 8 cents per 
gallon (§ 560-61). The oil is usually applied at the rate of J to J 
gallon per square yard, and the oiled width is generally 15 feet; and 



ART. 3] 



SURFACE OILING 



137 




Fig. 39. — Road Oiling-Machine. 




Fig. 40. — Machine Applying Asphalt Oii 



138 EARTH ROADS [CHAP. Ill 

therefore with the smaller values above, the oil may cost $88 per 
mile, and with the larger values $352. 

The cost of applying the oil will depend upon the length of the 
haul, the size of the tank, and the method of applying; and may 
vary from $50 to $150 per mile for machine application. There- 
fore, the total cost of oihng, including only slight preparation of 
the road surface, and excluding rent and depreciation of equipment, 
and also excluding general administrative expense, will vary from 
$148 to $527 per mile. 



il 



CHAPTER IV 
SAND AND SAND-CLAY ROADS 

Art. 1. Sand Roads 

243. As a rule roads on pure sand are the worst in existence, 
since they are good only when wet, and therefore are at their worst 
most of the year; while in most locaUties clay or loam roads are at 
their best most of the time. If the sand is fine, a dry sand road is 
worse than any muddy road. 

244. Drainage. Roads on pure or nearly pure sand require 
very different treatment from those on clay and loam. Dampness 
improves a sand road, while it damages a clay or loam road; and 
therefore the preceding rules for the drainage of loam or clay roads 
must be reversed for sand roads. Wet sand makes a better road 
than dry sand, and therefore draining a sand road is useless and 
possibly a damage. Of course, this is not true of quicksand, since 
that is improved by drainage; but there is very little, if any, of this 
material in roads. 

245. Grading. Sand roads are usually nearly level longitudi- 
nally; and hence need httle, if any, grading. They should not be 
crowned, since they do not need surface drainage. The traveled 
portion should be simply leveled off. 

246. Shade. While shade harms a loam or clay road, it im- 
proves a road of sand or broken stone, since it prevents the evapo- 
ration of the moisture from the road-bed. Therefore a sand road 
can be permanently improved by planting trees so as to shade the 
traveled way. They wiU prevent, in part, the drjong effect of the 
winds, as well as intercept the rays of the sim. 

247. Hardening the Surface. The great disadvantage of 
pure sand as a road material is the freedom with which the grains 
move one on the other; and therefore to improve a sand road grass 
should be encouraged to occupy all the space possible, since its roots 
will decrease the movement of the grains under the tread of the 

139 



140 SAND AND SAND-CLAY ROADS [CHAP. IV 

hoofs and wheels. It is an advantage if low growing bushy vege- 
tation occupies the surface clear up to the traveled way — both for 
the shade and for the binding effect of the roots and the leaves. The 
leaves fall into the ruts and also aid in binding the sand. 

Where no other recourse is possible, it is advantageous to have 
two roadways adjacent to each other, one of which is planted with 
grass while the other is in use. If the traffic is not very great, the 
effect of the grass will last for a year or two after the road is again 
used by the wheels. A fertihzer is sometimes appHed to stimulate 
a growth of grass upon the wheelway. In some localities the sand 
is so fine that it drifts fike snow, and fills the partially hardened 
way, in which case the road is improved by planting the roadsides 
with grass to prevent the sand from being blown into the road. 

A road on pure sand is improved temporarily by covering it 
with a thin layer of any vegetable fiber, as decaying leaves, straw, 
marsh hay, waste from sorghum mills (bagasse), fibrous or string- 
Hke shavings, etc. This fibrous material soon becomes incorporated 
with the sand and decreases its mobility; but the vegetable matter 
wears out and decays, and consequently the effect is only temporary. 
The length of time such expedients will last depends upon the 
climate and the amount of travel. 

248. In this connection it is a significant fact that the sand 
shoulders of a broken-stone road soon become firm and hard, owing 
to the infiltration of the fine dirt and stone dust washed from the sur- 
face of the roadway. The fine particles of dust between the grains 
of sand act mechanically to decrease the mobility of the sand, and 
to increase capillary attraction and diminish percolation, which 
in turn keeps the sand damp and still further decreases its mobihty. 
Apparently, then, the incorporation of fine dust in a sand road will 
improve it; but it will be difficult to procure sufficient dust for this 
purpose. 

Art. 2. Sand-Clay Roads 

250. A sand road is best when wet, and a clay road is worst when 
wet; but a road surface constructed of sand and clay mixed in proper 
proportions possesses the good quaUties of both the sand and the clay, 
and frequently is better then either. Such roads are called sand-clay 
roads, and give the best results where the ground is not subject to 
deep freezing. Materials suitable for the construction of sand-clay 
roads are found in greater abundance in the southern states than in 



ART. 2] SAND-CLAY ROADS 141 

any other portion of this country; and consequently sand-clay 
roads are much more common in that portion of the country, although 
sand-clay roads have been built to a considerable extent in several 
northern states. There are many locahties, particularly in the 
South, where sand-clay roads are the only improved roads which 
are economically possible. In many cases a sand-clay road gives 
good service at comparatively low cost of both construction and 
maintenance. 

Three distinct methods are employed in constructing sand-clay 
roads, viz.: (1) a natural mixture of sand and clay is placed on 
top of either a sand or a clay road; (2) a layer of sand is incorporated 
in the road-bed of a clay road; or (3) a layer of clay is added to a sand 
road. 

251. THE Design. The width and thickness adbpted will of 
course depend upon the travel and upon the money available. 
For a single track the improved width is usually 10 or 12 feet, and 
for a double track 14 or 16 feet. For a discussion of the super-eleva- 
tion and width on curves, see § 90 and 97, respectively. 

The thickness at the center varies from 6 to 10 inches, usually 
6 to 8 ; and at the sides 4 to 8, usually 4 to 6, but feathers out at the 
very edge. The crown should be J to f inch per foot of total width. 

252. Natural Mixtures of Sand and Clay. Sometimes a 
natural mixture of sand and clay is found in such proportions as to 
make an excellent road surface for moderate travel under most or 
aU weather conditions. 

The next chapter treats of gravel roads, and a special case of a 
gravel road is one in which a layer of natural cementing gravel is 
added to a clay or loam road; but such a form of construction will 
not be considered here. 

253. To Test the Sand-Clay Mixture. To determine the probable 
wearing power of natural mixtures of sand and clay proceed as 
follows: 

1. Examine the existing road to see if there are any portions 
that are reasonably good under all weather conditions, to identify 
the character of soil desired for other portions of the road. 

2. Observe out-crops of sandy clay or clayey sand. The best 
mixtures of sand and clay for road building purposes will stand at 
relatively steep slopes, will develop few surface cracks in drying, and 
will appear dense and firm in dry weather. 

3. Determine the percentage of clay and sand in the mixture. 
To do this, thoroughly dry a sample of the soil, weigh it, place it in 



142 SAND AND SAND-CLAY ROADS [CHAP. IV 

a vessel several times larger than the sample, fill the vessel with water, 
agitate the water, and pour off the muddy water. Before pouring 
off the water, allow it to stand a minute or two, so the sand may 
settle and thus prevent its being carried away with the clay. Repeat 
the washing until the water remains clear; and then dry the sand 
and weigh it. Fair results may be expected if the sand content is 
from 50 to 70 per cent; but the best results are obtained when 
the sand varies from 60 to 70 per cent; or in other words, for 
the best results about two thirds of the mixture should be sand. 
Further, the greater the proportion of coarse to fine sand the 
better.* 

4. Sometimes a natural mixture may be improved by combining 
it with another natural mixture or with nearly pure clay or pure 
sand. A determination of the sand and clay contents of the natural 
mixture will give some indication of the element needed to improve 
it; but the only way to determine it definitely is to make several 
trial proportions and test them. To determine which of several 
natural or artificial mixtures will probably give the best results in 
the road, proceed as follows: Mix the sample to a stiff mortar; 
spread a small quantity of each mixture upon a board or plate of 
glass to the thickness of about 1 inch; and with some improvised 
equivalent of a biscuit cutter, cut from each mixture two samples 
containing 1 to 2 cubic inches each. It is essential to cut only equal 
quantities from each mixture. Roll these samples between the palms 
of the hands into approximately true spheres; scratch a number on 
each; and then place them in the sun to dry. When thoroughly 
dried, one sphere of each sample should be tested dry and the other 
wet. To test a sphere dry, rub it lightly with the thumb, and if it 
has too much sand it will disintegrate rapidly ; while if it contains an 
excess of clay, it will speedily rub into dust. If it has a suitable 
proportion of sand and clay, it will simply become slightly glazed, 
and will offer considerable resistance to abrasion. To test the 
spheres wet, place them in a circle in a flat pan or dish, and gently 
pour enough water into the pan to cover them, being careful not to 
pour water directly upon any sphere. The specimens containing 
too much sand will break down first; those having an excess of clay 
will usually disintegrate next; and those having the best proportions 
will endure longest. These experiments will indicate the least 

* For a series of complete sieve analyses of fourteen samples of material from sand-clay 
roads that had given good service, and a discussion of the relative merits of the same, set 
Trans. Amer. Soc. of Civil Eng'rs, Vol. 77 (1914), p. 1465-75. 



ART. 2] 



SAND-CLAY ROADS 



143 



desirable mixtures, and will also show what other proportions 
should be tested. A second test of the most promising mixtures 
will probably indicate whether or not any of the samples are worthy 
of a trial in an experimental section of road. 

254. By proceeding as described above one may determine 
within comparatively narrow limits the possibility of successfully 
using any available mixtures of sand and clay for a road surface. 

255. Construction. When a suitable mixture of sand and clay 
is available, it is only necessary to add a layer of this material to a 
sand road or to a clay road. The road-bed on clay should be 
underdrained and crowned as described in Art. 1 of Chapter III, 
and the surface of the sand road should be prepared as stated in 
Art. 1 of this chapter. The amount of the initial crown will depend 
upon the thickness of sand and clay to be added. 

The sand-clay mixture is spread upon the road to the desired 
width and thickness (§251), and is smoothed with a scraping grader 
(§ 155) or drag (§ 206). Travel may then be admitted; but the 
road should not be considered finished until it has been thoroughly 
soaked by rains, harrowed to break up lumps, and again shaped 
with the scraping grader or drag. 

After the road has been in service for a considerable time, if it 
develops that either clay or sand is lacking in the surface, a thin layer 
of that element may be spread and be incorporated into the road-bed 
with a disk or toothed harrow. 

Finally the sand-clay road, if properly built, will become smooth, 
nearly dustless, and resilient; and under moderate travel should 
continue so without much, if any, expense for maintenance. 



h-j5b.5'H 



« Single Track -fO ft 

DoubleTrGck-f4ft 




-: ■ ■ * • • Flaf-orJ/fghtlyCrdm^^ 

Fig. 41. — Mixture of Sand and Clay on Native Subgrade. 



256. Sand on Clay Subgrade. The object in this form of 

construction is to incorporate sufficient sand with the clay subgrade 
to obtain a mixture of sand and clay that will fulfill the conditions 
stated in § 253. For the best results the amount of clay in the fin- 
ished road surface should not much exceed the amount required to 



144 



SAND AND SAND-CLAY ROADS 



CHAP. IV 



fill the voids in the sand. Ordinarily about two parts of sand to one 
part of clay gives satisfactory results. 



r-39oS^ 



DoubhTrxjck-fGff: 



^39oS'-^ 






Fig. 42. — Clay on Sand Subgrade. 



257. The Sand. The sand to be added to a clay subgrade 
should preferably be a coarse-grained pure siUca sand. Any sand 
containing any considerable percentage of mica is not desirable. 

For the best results, not less than 45 per cent nor more then 
60 per cent of the sand should be finer than that caught on a stand- 
ard No. 10 sieve, and coarser than .that caught on a No. 60 sieve; 
and that caught on No. 20, 40 and 60 sieves should be about equal 
to each other. 

258. The Proportions. The proportions of sand and clay can 
be determined approximately by finding the amount of water that 
can be poured into a vessel full of sand. To do this determine 
the weight of water required to fill any suitable vessel; and then 
fill the vessel with sand. Next determine the weight of water that 
can be poured into the vesselful of sand. For example, if the pail 
holds 12.4 lb. of water, and 3.5 lb. of water can be poured into the 
pailful of sand, then the voids in the sand are: 3.5 -^ 12.4 = 28 
per cent. Therefore in the finished road the proportion of clay should 
be about 28 per cent, and that of sand about 72 per cent. This 
proportion and others differing shghtly therefrom should be tested 
by the method described in paragraph 4 of § 253. 

However, since exact mathematical proportions are not possible 
in incorporating the sand with the clay in the road surface, mathe- 
matical refinement in these experiments is inappropriate. 

259. The Thickness. For average rural-road travel, the depth 
of the sand-clay surface should be about 6 to 8 inches at the center 
and 4 to 6 inches at the edges of the traveled way feathering out 
on the shoulders; and hence the thickness of the layer of sand 
to be added to the road should be roughly two thirds of the above 
depth, the exact thickness depending upon the best proportion of 
sand and clay as determined by the method described in § 253. 



ART. 2] SAND-CLAY ROADS 145 

260. Construction. The surface of the clay road is shaped up as 
described for an earth road (§ 129-31), and is then thoroughly plowed 
to a depth of 6 or 8 inches according to the thickness of sand to be 
added. Next the thickness of sand determined as above is spread 
upon the surface and leveled down with the scraping grader or the 
road drag. The road is then plowed again, as deep as possible, to 
mix the clay and the sand;' and after this plowing the sand and clay 
are further mixed by harrowing with a disk harrow, which can be 
done best when the road is wet. Attempting to mix the materials 
dry is usually unsuccessful. After the sand and clay are thoroughly 
mixed, the surface is smoothed and crowned with the blade grader 
or the road drag, and travel is admitted to complete the mixing and 
to compact the road. While the road is new it should be watched 
carefully, and the surface should be kept free from ruts and saucer- 
like depressions by going over it when necessary with the scraping 
grader or the V road leveler. When the road has begun to solidify, 
the road drag is not very effective — at least neither the split-log nor 
the plank drag. It will likely be necessary to add clay in spots where 
the road surface is loose, and sand where it is sticky. Probably 
the road will not arrive at its best condition for a year or two or at 
least not until after several long-continued wet spells during which 
the travel will thoroughly consolidate the road. 

261. Clay on Sand SUBGRADE. The clay is added to serve 
as a binder to hold the grains of sand together. For the form of 
construction under consideration here, clay is the only material 
available for permanent effect. For the proportions of clay and sand 
to be attained, see § 253. 

262. The Clay. Clay varies more in its suitability for road build- 
ing purposes than sand; and it is difficult to determine in advance 
the result of a service test in the road. 

All clays contain more or less sand, and as the clay is to serve 
as a binder for the sand, the less sand the clay contains, that is the 
more nearly it is a pure clay, the better; and hence loam, which 
is a mixture of clay, sand, and vegetable matter, is not the most suit- 
able for this purpose. 

The less the clay is affected by the presence of water the better. 
Clays are known as slaking and non-slaking. The former absorb 
water freely and slake or fall to pieces when put into water, some- 
what Uke a piece of quick-lime; and are deficient in binding power, 
and hence are undesirable as a binder for a sand-clay road. 

To compare the slaking qualities of several clays, make small 



146 SAND AND SAND-CLAY ROADS [CHAP. IV 

balls of each of approximately the same size by rolling between 
the hands, leave the balls in the sun or put them into an oven until 
they are well dried out, and then place them under water. The 
ball which holds its shape longest has the highest resistance to 
slaking, and contains the clay most suitable for use as binder in a 
sand-clay road. To make a fairly trustworthy comparison the 
samples should contain substantially the same proportion of sand; 
and therefore the percentage of cand in each sample of clay should 
be determined (see § 253) before beginning the above test, and sand 
should be added so as to give all samples the same proportion of 
sand. 

The above method of testing may be employed also to determine 
the slaking qualities of the clay when mixed with different propor- 
tions of sand, and therefore may afford valuable information in fix- 
ing the proportions of clay and sand to be used in the road surface. 

Other things being equal, the clay which shrinks least in drying 
out is best suited for use in a road surface. The relative shrinkage 
may be determined by observing the balls used in the test above, 
while they are being dried out before being immersed. 

263, The Construction. The road-bed should be provided with 
side ditches and be graded as described for earth roads (§ 129-31), 
except that the surface should have but little, if any, crown. Then 
spread a layer of clay of such thickness that when thoroughly mixed 
with the sand of the road-bed, the mixture will have the required 
depth, — 6 or 8 inches as the case may be. The thickness of the loose 
clay required will usually be a Uttle greater than one third of the 
ultimate thickness of the combined sand and cla3^ The exact pro- 
portion of clay to secure this condition is to be determined as de- 
scribed in § 253. 

After the clay has been spread and leveled off with a road drag, 
the clay and the sand are to be thoroughly mixed by successively 
plowing and then harrowing with a disk harrow. Roughly the 
plowing should extend into the sand to twice the depth of the layer 
of clay added. It is better at first to have too httle sand rather than 
too much, for it is easier to correct the proportions by adding sand 
from the subgrade then by hauhng clay from a distance. When 
the sand and clay have been thoroughly mixed in the correct propor- 
tion, the road should be properly shaped by the use of a scraping 
grader or road drag, and then travel may be permitted. After the 
first soaking rain, plow and harrow the surface again until the sur- 
facing material practically becomes mud, after which shape up 



ART. 2] 



SAND-CLAY ROADS 



147 



the surface and keep it in shape by repeated dragging until it has 
dried out and is thoroughly compacted. At this stage the road 
roller should not be used, since it will harden only the surface and 
prevent the travel from consoHdating the mixture from top to bottom. 
The crust formed by the roller will carry the travel until the first 
wet spell, and then it will cut through and the road will break up; 
and nothing permanent will have been gained by the use of the 
roller. 

The road should be watched carefully for several months, and ruts 
and other depressions should be filled by the use of the steel road 
drag or the scraping grader. Any deficiencies in sand or clay that 
are revealed should be corrected by adding the lacking ingredient. 

264. Cost. In the Southern states the cost of constructing a 



TABLE 22 

Cost of Sand Clay Roads* 

Exclusive of grading and materials 





Mixture of 

Clay and 

Sand. 


Sand on Clay 
Subgrade. 


Clay on Sand Subgrade. 


Items. 


Brook- 

ville. 
Fla. 


Gray 
Head, 
Miss. 


Mos- 
cov/. 
Miss. 


Jack- 
son, 

N. C. 


Pear- 
shall, 
Tex. 


San 
An- 
tonio, 
Tex. 


Tar- 
boro, 
N. C. 


Sayre, 
Okla. 


Length surfaced, miles 

Width graded, feet: 

Cuts 


0.45 

28 
20 

16 

660 

0.75 

3 

830 
0.50 

7 

$0,175 
.50 

.031 


2.19 

22 
22 

16 

1700 

0.125 

6 

2 300 

0.10 

6 

$0.20 
.50 

.010 
.223 
.344 

.003 
.010 

.004 
.006 


0.78 

30 
30 

17 

1 524 
1.5 

7 


0.45 

30 
30 

14 

890 
1.00 

7 


0.79 

26 
26 

15 


1.00 

40 
26 

16 


2.50 

22 
22 

18 


0.75 
28 


Fills 


28 


Width surfaced, feet 

Materials: 


14 


Distance hauled, miles . . . 










Depth applied, inches. . . . 










1556 

0.19 

8 

$0.12 
.30 

.0064 

.091 


1 815 
0.057 

7 

$0.15 
.345 

.0088 

.072 


2 815 

$0.08 
.24 

.0018 

.005 


1 883 


Distance hauled, miles. . 






1 42 








8 


Wages per hour: 

Laborers 


$0.10 
.25 

.003 
' ■ ; 49 ' 


$0,125 
.35 

.002 

0.29 
.84 


$0 16 


Teams 

Cost: 

Subgrade, per sq. yd 

Stripping surfacing ma- 


.30 

.0096 
134 


Hauling sand, per sa. yd 


.425 
.374 

.019 
.0035 

.0035 
.0157 




Hauling clay, per sq. yd. . 
Spreading material, per 


.914 

.032 
.0017 

.0005 
.003 


I .286 
.0069 
.0015 


.255 

.0178 
.0024 

.0022 
.0007 


567 


.007 
.006 


.077 

.002 
.003 


.072 


Mixing sand ]and clay, per 
sq yd 


.007 


Final shaping, per sq. yd . 
General expense, per sq. yd . 




Total cost, per sq.yd. 


0.198 


0.082 


0.105 


. 233 


.121 


.089 


.036 


.187 



* Constructed by U. S. Office of Public Roads and Rural Engineering, Bui. No, 463 
(1917), p. 45. 



148 SAND AND SAND-CLAY ROADS [CHAP. IV 

16-foot sand-clay surface, exclusive of grading, usually ranges between 
$500 and $1500 per mile and nearly proportionally for other widths. 
For details of the cost of some such roads, see Table 22. 

In Michigan, which state seems to have more sand-clay roads 
than any other state except Georgia, the cost of a well-built 
9-foot sand-clay road consisting of 6 inches of clay on a sand sub- 
grade ranges from $1,000 to $1,800 per mile. 

265. Maintenance. The sand-clay road is reaUy a superior 
type of earth road; and therefore aU that has been said in Chapter 
III concerning the maintenance of earth roads applies also the sand- 
clay surfaces. As in the case of ordinary earth roads, economical 
maintenance depends largely upon proper original construction. The 
use of too fine sand and- the insufficient mixing of the sand and clay 
are the common defects of construction that should be remedied by 
proper maintenance. 

The surface should be kept smooth and properly crowned by the 
use of the road drag, particularly after severe or long-continued 
wet spells. If a hole forms because of an excess of clay, it should 
be filled mainly or entirely with coarse sand, after first loosening the 
material in the bottom of the hole with a pick so that the new mate- 
rial will bond with the old. Sometimes the fine sand washes to the 
side of the road and leaves an excess of clay, in which case a thin 
layer of new coarse sand should be spread upon the surface when it 
is soft or at least wet. The sand that has washed out should never 
be used again. 

If the whole surface has a tendency to rut and form holes in 
wet weather, it usually means that too much clay has been used in 
the construction of the road; and it may then be necessary to cover 
the entire surface with a layer of sand and harrow it in. If, on the 
other hand, the surface is too sandy, clay must be added in the same 
way. 

If lack of proper dragging has allowed the road to become badly 
worn, then it must be plowed up with a rooter plow, after which it 
should be harrowed, preferably with a disk harrow, and be re-shaped 
with a grader. 

266. The ability of a sand-clay road to carry travel, particularly 
motor-driven vehicles, is indicated roughly by Table 23, page 149. 

267. Apparently, in the Southern States, representative sand-clay 
roads are maintained in reasonably good condition at an expense of 
$5 to 110 per year per mile, the chief or sole expense being for 
dragging. 



ART. 2] 



SAND-CLAY ROADS 



149 



TABLE 23 
Approximate Travel on Sand-clay Roads in Georgia j 



Type of Vehicle. 


Average Numbers of Vehicles both Ways, 
per Day. 


"-5 


XJ 
^ 




< 


>> 


s 

•-5 


>> 


fcit 
3 




O 


o 


d 


Horse-drawn: 


20 

60 

60 

4 

144 

10 
6 
2 

2 

20 
12 


30 

90 

90 

6 

216 

10 
6 
2 

2 

20 

8 


35 

100 

120 

6 

261 

15 
8 
4 
3 

30 

10 


25 

75 

75 

4 

179 

20 

10 

6 

4 

40 

18 


20 

60 

60 

4 

144 

20 

10 

6 

4 

40 

22 


20 

60 

60 

4 

144 

30 
15 

8 
2 

55 

28 


20 

60 

60 

4 



144 

30 
15 

8 
2 

55 

28 


25 

70 

70 

5 

170 

20 

10 

8 

2 

40 

19 


40 

120 

120 

8 

288 

30 

15 

8 

4 

57 

14 


40 

120 

120 

8 

288 

30 
15 

8 
4 

57 

14 


25 

75 

75 

4 

179 

20 

10 

6 

2 

38 

26 


?0 




40 


2-horse wagon (net load 1,500 lb.) 

4-horse wagon (net load 3,000 lb.) 

Total 


40 
4 

104 


Motor-driven: 


10 


4-passenger automobile 

6-passenger automobile 

Trucks (net load 1,500 lb.) 


6 

2 


Total 


?n 




16 







t Trans. Amer. Soc. of Civil Eng'rs, Vol. 77 (1914), p. 1492. 



CHAPTER V 
GRAVEL ROADS 

270. Gravel may be defined as a mass of small, more or less 
rounded fragments of stone which have been broken out and shaped 
by the action of water or ice. When properly used gravel makes 
an excellent road surface; and is much used on account of its wide 
distribution, the ease with which it can be appUed, the good results 
obtainable under widely varying conditions of soil, cUmate and travel, 
and the low cost of construction and maintenance under a moderate 
amount of travel. Many gravel roads have been poorly constructed 
or inadequately maintained, or over-burdened with travel; and as 
a consequence many people beheve the building of gravel roads a 
waste of money under any condition. Nevertheless good gravel 
roads have a large field of usefulness. Gravel roads constitute 
about one third of the total mileage of improved roads in the United 
States; and in 1914 constituted 41 per cent of the state-aid roads. 

A gravel surface is most suitable for country highways not having 
exceedingly heavy traffic, for unfrequented streets in villages and 
small cities, and for park roads. 

Art. 1. The Gravel 

271. REQUISITES FOR ROAD GRAVEL. To be suitable for 
road-building purposes, gravel should fulfill the following conditions: 
1. The fragments should be so hard and tough that they will not be 
easily ground into dust by the impact of wheels and hoofs. 2. The 
pebbles should be of different sizes, each in the proper propor- 
tion. 3. There should be intermixed with the coarser particles 
some material which will cement and bind the whole into a soHd 
mass. 

272. Durability. From the nature of its origin, it is apparent 
that gravel may differ widely in the nature of the stones composing 
it. Not only do different gravels differ from each other, but any 

150 



ART. 1] THE GRAVEL 151 

particular gravel may be composed of fragments of a variety of 
rocks. Having been transported a considerable distance by water 
and ice, gravel is usually fairly durable, since the softer and more 
friable fragments have been worn away. In many parts of the 
country the rocky fragments transported by water and ice are more 
durable than any of the native rocks.* 

273. Sizes. If the pebbles are too large, the road will not be 
homogeneous, and the large stones will work to the surface under the 
action of traffic and frost; but, on the other hand, if the pebbles 
are too small, the gravel will partake too much of the character of 
sand, and will be difficult to bind properly. The best results are 
obtained when the largest pebbles are not more than f to 1 inch, or 
at most 1| inches, in greatest dimension. With stones larger than 
1 inch, it is difficult to keep the surface from breaking up when dry. 
Small gravel makes a pleasanter road to ride upon and one that is 
easier to keep in order. If stones larger than 1| or 2 inches are 
present in the gravel, they may be screened out and used in the 
foundation (§303). 

It is desirable that the several sizes should be so proportioned 
that the smaller ones are just sufficient to fill the interstices between 
the larger ones, since then less binder is required. The binder is 
usually the least durable ingredient, and hence the less there is of it 
the better. Gravel can often be improved by screening — either co 
remove an undesirable size or to separate it into several sizes 
afterward to be combined in new proportions. The proper pro- 
portion depends upon the nature of the gravel — whether the binding 
material is already present in the form of dust, or whether some of 
the pebbles must be crushed to produce the binder. 

274. Binder. The most important requisite for good road- 
building gravel is that it shall bind or pack well. If it does not pack 
well, the wheels will sink into the gravel and increase the tractive 
resistance, and the rain water will penetrate the road-bed and soften 
it. To bind well, the several fragments should be in contact with 
one another at as many points as possible, in order that they may 
be firmly supported, and that friction may act to the best advantage 
to resist displacement. To secure contact at every point, aU the 
interstices between the fragments should be filled — those between 
the large pebbles, with small pebbles; those between the small 
pebbles, with sand grains; and, finally, those between the sand 

* For a discussion of the merits of the principal stones for road-building purposes, see Art. 1. 
Chapter VI. 



152 GEAVEL ROADS [cHAP. V 

grains, with some finer material, called a binder. The binding 
material must be very finely divided, so that it can be worked into 
the smallest interstices; and for this reason, it is the least durable 
part of the gravel, being easily washed out or blown away. For 
the best results, then, the sizes of the coarser particles should be so 
adjusted as to require a minimum amount of binder. 

The binding material may consist of clay, loam, silica, stone dust, 
iron oxide, etc., or some other ingredient which will crush under traffic 
and furnish a fine dust. 

Clay is by far the most common binding material; but the only 
recommendations for it are (1) that it is easily reduced to an im- 
palpable powder by the action of wheels or by water, and (2) that 
it is often found already mixed with the gravel, and (3) that if it 
must be artificially mixed, it is plentiful and cheap. Clay is an un- 
desirable binder, since its binding action depends in a large measure 
upon the state of the weather. During a rainy period it absorbs water 
and loses its binding power, and the road becomes soft and muddy; 
while in dry weather it contracts and cracks, thus releasing the 
pebbles and giving a loose surface. Clay is also very susceptible 
to the action of frost; and consequently when the frost is going out, 
a gravel road with a clay binder ruts up badly and frequently breaks 
entirely through. When the weather is neither too damp nor too 
dry, a gravel road with clay binder is very satisfactory. The clay 
should be no more than enough to fill the voids in the pebbles and 
sand, and for a good road-gravel should not exceed 15 to 20 per cent 
of the mass. Not infrequently much greater quantities of clay are 
present. This surplus may sometimes be removed by screening; 
but often it can be removed only by washing — a process which is 
usually so expensive as to be prohibitive. 

Loam is chiefly clay mixed with sand and a little vegetable 
matter, lime, etc.; and as a binding material has all the charac- 
teristics of clay. 

A very finely divided silica, easily mistaken for clay, is occa- 
sionally present in gravel, and makes an excellent binding material. 

Iron oxide is frequently found as a coating on the pebbles in 
such quantities as to cement them firmly together. These ferru- 
ginous gravels when broken up and put upon a road, will again 
unite — often more firmly than originally, because of the greater 
pressure — and form a smooth hard surface, impervious to water. 
They are much used in road building, gravel from Shark River, 
N. J., — much used around New York City — and that from the Ohio 



ART. 1] THE GRAVEL 153 

river near Paducah, Ky., — largely used in the neighboring states — 
being examples. 

275. Comparatively coarse gravel frequently contains some 
other ingredients, as, for example, fragments of limestone or shale, 
which under the action of traffic and the weather reduce to a powder 
and form a good binding material. Sometimes gravel contains bits of 
iron-stone (clay cemented with iron oxide) in the form of thin flat 
chips which break and crush easily under the wheels, and if present 
in any quantity make a most excellent binding material. 

276. The binding action referred to in the preceding discussion 
is mechanical; and we come now to the consideration of an action 
not yet well understood, but which for the present at least will be 
called chemical action. Experiments seem to prove that if fine 
powder of certain stones is wetted with water and subjected to 
compression, a true chemical cementation takes place. Conse- 
quently some stones when broken into small fragments, wetted and 
traversed by heavy wheels or by a road-roller will be cemented 
together to a considerable degree. This cementation is due to the 
fact that the friction of one small piece of stone upon another pro- 
duces a very fine powder at the point of contact, which when wetted 
and compressed, forms a weak cement. Owing to the rounded 
surfaces of water-worn pebbles, this cementing action is much less 
with gravel than with rough angular fragments of broken stone; 
but with gravel composed of undecayed rocky fragments this action 
takes place to a considerable degree. As a rule, pebbles of bluish 
color will thus cement together, while reddish or brown ones will 
not, which accounts in part at least for the well known superiority 
of blue gravel for road purposes. Trap rock possesses the property 
of cementation in a high degree, and hence trap gravel is a very 
excellent road-building material. Limestone possesses a fair de- 
gree of cementation, but is too soft to wear well. Quartz wears 
well but produces little or no dust for cementation, and besides its 
surfaces are so smooth and hard that the binder has but little effect; 
and therefore it rarely happens that a gravel of which more than 
one half of its bulk is white quartz pebbles proves to be a good road 
gravel. 

The cementation of rocky fragments is much more important in 
a water-bound macadam road than in a gravel one, and therefore 
the subject will be more fully considered in Chapter VI. 

277. The binding elements heretofore discussed exist naturally 
in the gravel; but gravels are often found that do not contain any 



154 



GRAVEL ROADS 



[chap. V 



binding material, and in such cases it is necessary to add some 
cementing material. 

Clay, shale, hard-pan, marl, loam, etc., are often used for this 
purpose, chiefly because they are so plentiful and easily appHed; 
but none of them are suitable for the purpose, as they all have the 
characteristics of a clay binder (see § 274). With any of them, it 
is difficult to keep the gravel from breaking up — particularly under 
heavy traffic. 

In some locahties a poor iron ore is found, which, when mixed 
with gravel, makes an excellent binder and gives a smooth hard 
road surface. Bog iron-ore, which occurs in marshes, is usually 
very good for this purpose. 

The fine dust from a stone crusher, when mixed with gravel, will 
bind it together; but it is seldom feasible to use stone dust on 
account of the expense. When this method of binding gravel is 
resorted to, the construction partakes of the character of a water- 
bound macadam road — a subject foreign to this chapter (see Chapter 
VI). The chief difference between a gravel and a crushed-stone 
road is in the thoroughness of the binding. The binding of a gravel 
road is due chiefly, and usually solely, to the mechanical action of 
the binder; while the binding of the broken stone is due to both the 
mechanical and the chemical action of the binder, and both are 
stronger with rough angular fragments of broken stone than with 
water-worn pebbles. 

278. Distribution of Gravel. The gravel beds of the 
glacial drift furnish excellent road-making materials. The glacial 
ice sheet, often a mile or more thick, covered New England and 
Canada and all of the United States north of an irregular line start- 
ing on the Atlantic Coast a little south of New York City and run- 
ning thence successively to the southwest corner of the State of New 
York, to Cincinnati, to a point a Uttle north of the mouth of the 
Ohio river, to the mouth of the Missouri river, to Topeka, Kansas, 
thence north and west a little west and south of the Missouri river 
to the head waters of that stream, and thence west to the Pacific 
ocean. All of the area north of the above described line was cov- 
ered with the ice sheet except small portions of southeastern Minne- 
sota, northeastern Iowa, northwestern IlHnois, and a considerable 
portion of southwestern Wisconsin. As this ice sheet crept to the 
southward, it rent great quantities of stone from the bed rocks; and 
these materials were borne southward, either in the slow-moving 
ice or hurried along by the violent currents of water which swept 



ART. 1] THE GRAVEL 155 

forward to the margin of the ice field. Thus impelled the under- 
ice streams were able to bear toward the margin of the glacier great 
quantities of stone. The original range of the glacial gravels has 
been greatly extended here and there by the streams, which, flowing 
southward beyond the drift belt, have often carried quantities of 
the hard detritus for many miles beyond the Hmits of the ice- 
field. 

Unfortunately the glacial gravel deposits have not been studied 
from the point of view of the road-maker. However, it is known 
that east of the Hudson river the glacial supply of road gravels is 
only here and there of economic importance, for in most of that field 
the glacial waste lies on native rocks which are suitable for road- 
making; and that from the Hudson to the Mississippi, the glacial 
deposits of bowlders and gravel afford better road-building mate- 
rials than any of the native rocks. Glacial gravels exist in consid- 
erable quantities in western Pennsylvania, in the greater part of 
Ohio, in northern Indiana, and in northern Illinois, and to some 
extent in several of the states of the Northwest. 

279. South of the glacial district, the rocks exposed to the 
weather have decayed by a process of leaching, which in many cases 
has removed strata hundreds of feet thick. The rocky portion is 
removed in proportion to its solubility; and, as a result, there are 
often left concretions of cherty matter which were originally con- 
tained in beds of limestone. This cherty residuum of flinty mate- 
rial generally lies in a comparatively thin sheet of fragments min- 
gled with sand and clay; but occasionally it is found in deposits 
from which the clay and sand have been removed by recent or 
ancient streams, leaving the material well suited for spreading upon 
a road. Sometimes this cherty residuum is found in layers of 
fragments many feet thick, and is valuable for road-building in a 
locaHty where more suitable material is scarce. The presence of 
chert is often revealed by the gullies in the plowed fields and along the 
streams. In some localities very good roadways are constructed 
simply by shoveling these fragments from the stream beds and 
depositing them on the road.* 

This cherty deposit is a valuable road material in the southern 
portion of the Appalachian mountains, and along the Ozark foot- 
hills in southern Illinois (particularly in Alexander and Union 
counties), in southern Missouri, and in northern Arkansas. Chert 
is found in some of the states of the Northwest where the glacial 

* For a discussion of chert as a road-building material, see § 295. 



156 GRAVEL ROADS [CHAP. V 

erosion was small, so that the rocks that had decayed before the 
glacial time were not entirely removed. In southwestern Arkan- 
sas the gravels consist of fragments of novacuUte or razor stone — a 
material of nearly the same geological origin and physical character- 
istics as chert. In many places in that state the novaculite gravels 
form extensive beds, 20 or more feet thick. At the southern 
extremity of the Appalachian mountain system is a wide-spread 
deposit of gravel, termed the La Fayette formation, whose geologi- 
cal origin is not determined. This deposit often attains a thickness 
of 40 to 50 feet, and is a valuable source of road-building material. 

280. If gravel be defined as material prepared by nature ready 
to be laid upon the road, then a few words are in place here concern- 
ing iron ore. In some localities there are low-grade iron ores 
which, owing to the admixture of various impurities, are unfit for 
use in making iron, but may be valuable for road building. These 
low-grade ores are widely distributed; and generally wherever 
limestone occurs below a considerable thickness of sandstone, the 
upper portion of the limy layer will be found to contain iron, and 
will probably be a fair road material. A lean iron ore is frequently 
found in marshes; and this variety, known as bog ore, usually 
makes excellent roads, since it crushes readily and gives a smooth 
hard surface. 

281. Exploring for Gravel. In searching for gravel in the 
glaciated district, the following suggestions by Professor Shaler * 
will be useful: 

'* In the process of retreat of the ice, the deposits which it left 
were accumulated under several quite diverse conditions. One of 
these produced the till, or commingled coarse and fine materials, 
which had been churned up into the ice during the time of its 
motion, and came down, when the melting occurred, as a broad, 
irregularly disposed sheet which, with rare exceptions, is to be 
found in all parts of the glaciated district, save where it has been 
swept away by streams. 

" Again, from time to time during the closing stages of the ice 
age, the prevaiUng steadfast retreat of the ice was interrupted by 
pauses or re-advances. In these stages there was formed along the 
margin of the ice-field what is called a frontal moraine, composed of 
debris shoved forward by the glacier or melted out of it along its 
front. These moraines are in most cases traceable, where they 
have not been washed away or buried beneath later accumulations, 

* American Highways, N. S. Shaler, Professor of Geology, Harvard University, p. 71-73. 



ART. 1] THE GRAVEL 157 

in the form of a ridge-like heap of waste, which, as we readily note, 
contains much less clay and sand and therefore a larger proportion 
of gravel and bowlders, than the sheet-like deposit of till above 
described. In some cases these moraines are very distinct features 
in the landscape, appearing, from the number of large bowlders 
which they expose, much like ruined walls of cyclopean masonry. 
More commonly they are found in the form of slight ridges, which 
may be covered with fine material, but commonly exhibit here and 
there projecting bowlders. In general it may be said that the 
moraines afford much better sites for pits from which road mate- 
rials are to be obtained than the till, and this because of the pre- 
vailing absence of clay and sand in the deposits. 

" Here and there in almost all glaciated districts, especially in 
the valleys of the greater streams, there may be found narrow ridges, 
often of considerable height, and almost always extending in the 
direction of the ice movement. These ridges are generally termed 
by geologists eskars, and often have a tolerable continuity for 
scores of miles at right angles to the ice front. A section of them 
shows generally a gravelly mass, nearly always free from clay and 
often containing little sand, though occasionally there is an abun- 
dance of large bowlders, which have a prevailing rounded or water- 
worn form. These eskars were doubtless formed in the caves be- 
neath the ice through which the ancient sub-glacial streams found 
their way. These under-ice rivers were much given to changing 
their position, and as a stream lost its impetus it was apt to fill its 
ancient arched-way with debris, which in its time of freest flow 
would have been sent forward to the ice front. At many places in 
New England and in New York these eskars contain large and use- 
ful deposits of gravel, and also occasionally quantities of bowlders 
well fitted for crushing as regards their size and hardness. In the 
Western States, because of the general coating of deep soil, these 
eskars are less easily found; but they exist there, and should be 
sought for. 

*' Where the eskars terminate, as they commonly do, on a 
morainal line, there is almost invariably found, immediately in 
front of their southern terminations, a delta-like deposit which, 
though generally composed in large measure of sand, frequently 
contains near the moraine extensive accumulations of useful gravel 
and small bowlders which are fit for crushing. 

" Information may be had from the banks of streams, where by 
chance they have cut below the deep coating of fine materials. The 



158 GRAVEL ROADS [CHAP. V 

existence of any distinct up-rise of the surface affords some reason 
to expect that the coarse glacial waste may be at that point not 
very deeply hidden." 

282. When a gravel road is to be built, if the local gravel resources 
have not already been thoroughly explored, every reasonable effort 
should be made to ascertain the extent and character of the available 
deposits of gravel. To test a gravel deposit, test holes or wells should 
be sunk at regular intervals over the deposit. These holes should 
be large enough for a man to get down into them and to examine 
the gravel in place and to collect samples. Care should be taken that 
the samples are truly representative. Note should be made of the 
amount and character of the overlying material, of the depth of the 
gravel deposit, and of the dip of the strata. 

283. Characteristics of Different Gravels. Any gravel 
which stands vertical in the bank, showing no signs of slipping 
when thawing out in the spring, requiring the use of the pick to 
dislodge it, and falling in large chunks or soHd masses, is sufficiently 
clean and free from clay for use on the road, and usually contains 
just enough cementing material to cause it to pack well. 

Pit gravel usually contains too much earthy material, and can 
be greatly improved by screening. Gravel is still being deposited 
in drifts and bars by streams, and this will be found to partake of 
the character of the pit gravel of the locaUty, except that it gen- 
erally contains less clay, and may have an excess of sand. This 
is often called river gravel, and is one of the best sources of road 
material. Lake gravel varies greatly in character. It is usually 
free from earth and contains sufficient sharp sand to pack well; 
but is Hable to be slaty — an undesirable quality. 

284. Composition of Representative Gravels. In an endeavor 
to determine the composition necessary for a road-building gravel, 
samples were obtained of a number of gravels that had given satis- 
factory service in the road. The samples in each case were selected 
by a person thoroughly conversant with the use of that particular 
material, and are believed to be fairly representative. 

Table 24, page 160, shows the sieve analysis of these gravels. 
Each sample was first washed in successive waters until the water 
remained clear, and then the wash water was allowed to stand until 
the matter in suspension was precipitated. The precipitate was 
dried in an oven to a constant weight and then weighed; and the 
washed gravel was air-dried, and then sifted and weighed. The 
per cent of voids in the washed gravel was obtained by gently ram- 



ART. 1] THE GRAVEL 159 

ming the gravel under a measured quantity of water in a small metal 
cylinder, the ramming not being severe enough to crush any of the 
pebbles or fragments. 

Table 25, page 161, shows the results of a mineralogical analysis 
of such of these gravels as had passed a screen having |-inch meshes. 
The matter recorded in Table 24 as being in suspension is called 
clay in Table 25, although part of it was doubtless organic matter 
and part fine sand, but the error is not material. 

285. To study these gravels further, each wiU be considered in 
order. 

1. Urhana. This is a screened drift gravel obtained near Ur- 
bana, Champaign Co., 111., which has been used in a few instances 
on private driveways. Table 25 shows only 3.8 per cent of clay 
present, which will have only a smaU binding effect. There is 
7.6 per cent of iron oxide (Fe203) in the clay, but there is so small 
a proportion of clay in the gravel that the iron contained in it will 
have an inappreciable binding effect. The principal source of binder 
is, then, the 65 per cent of ferruginous limestone. Limestone itself 
when pulverized makes an excellent binding material. However, 
in this case only a small part of the limestone is in the form of flat 
chips that may be easily crushed under the wheels, but the most of 
the fragments are rounded and not easily crushed except by compara- 
tively heavily loaded wheels. There is only a small per cent of 
crystalhne rocks present, and these are hard and not readily crushed, 
and consequently can not materially affect the binding quaUties of 
the mass. The gravel also contains 22.2 per cent of quartz; but 
this material is very hard and not easily crushed, and besides its 
dust is almost wholly devoid of cementing properties. Both the 
quartz and the crystalline rocks are quite sharp and angular, which 
is a very desirable condition, and aids the binding action of the 
clay and the limestone dust. This gravel packs slowly in the road, 
particularly under the light traffic of a private driveway; but under 
moderate traffic makes a fairly good road, and is not much affected 
by freezing and thawing. 

2. Decatur. This is a gravel much used on the country roads 
near Decatur, Macon County, 111., with satisfactory results. This 
gravel has a comparatively large amount of fine sand. An examina- 
tion of Table 25 shows that it contains more than twice as much 
clay as the Urbana gravel, but only about one third enough to 
fill the voids. A considerable portion of the limestone both of 
the pure and the ferruginous — a total of 30 per cent, — ^i.s in thin 



160 



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CHAP. V 





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162 GRAVEL ROADS [CHAP. V 

friable chips, and is easily crushed by the traffic, thus making an 
excellent binder. The ferruginous limestone contains an unim- 
portant proportion of iron; but the ferruginous sandstone is heavily 
charged with iron oxide, which makes a good cementing material. 
This gravel makes a smooth, hard surface, reasonably free from 
dust in the summer and mud in the winter. 

3. Lexington, This gravel is used with entire satisfaction in 
and around Lexington, McLean County, 111., for country highways. 
Notice that the clay is equal to only one seventh of the voids. 
Nearly all of the 21 per cent of ferruginous limestone consists of 
thin chips which are easily crushed by the traffic. Some binder is 
probably obtained from the 58 per cent of siliceous limestone. The 
per cent of crystalUne rocks present is very small, and can not 
materially affect the quantity of the gravel. The amount of quartz 
is less than in the preceding gravels, and is an unimportant ele- 
ment. 

4. Rockford. This gravel has given satisfactory service in Rock- 
ford, Winnebago County, 111., probably under more exacting con- 
ditions than any of the preceding. This is considerably the coarsest 
gravel in Table 24. Notice that this gravel contains, roughly 
speaking, only about one tenth enough clay to fill the voids. The 
chief source of binder is the limestone which exists in the form of 
pebbles, but contains no considerable amount of iron or silica. The 
basic crystalUne rocks by decomposing may furnish a little binder; 
but as they are round hard pebbles, not easily crushed, the binder 
derived from this source can be of no practical importance. Very 
little cementing material may be derived from the iron conglomerate 
or from the limestone and quartz conglomerate. 

5. Peekskill. This gravel is from Roa Hook, a '' point " in the 
Hudson river near Peekskill, N. Y., and is much used in and around 
New York City, where it is considered one of the best road gravels. 
Notice that the clay is less than one thirtieth of the volume of the 
voids. Considerable binding material is doubtless derived from the 
ferruginous limestone, which contains a comparatively small per cent 
of iron. The iron in the ferruginous sandstone is too small in amount 
to be appreciable. Some binder is doubtless derived from the meta- 
morphosed rocks containing iron, silica, and mica. Notice that there 
are nearly 30 per cent of crystalline rocks, which upon being finely 
pulverized will furnish an excellent cementing material, particularly 
after being decomposed. This gravel requires considerable rolling 
with a heavy roller to crush the several ingredients and liberal 



ART. 1] THE GRAVEL 163 

sprinkling to work the pulverized material into the voids, before the 
mass binds. All other gravels in Table 24 bind and make fair roads 
under ordinary traffic. 

6. Buck Hill. This gravel was obtained from the Buck Hill pit 
at Tuckahoe, N. J. It was recommended as a representative 
gravel by Hon. Henry I. Budd, State Commissioner of PubUc 
Roads of New Jersey. This gravel consists chiefly of clay and 
partially rounded quartz pebbles. The metamorphosed rock is 
angular and friable. The clay is probably enough to fill the voids 
when the gravel has been compacted by traffic. This is the first 
of the samples in which the iron contained in the clay is appreciable, 
and the iron doubtless has an important part in binding the road. 
This gravel is used for road building without rolling. 

7. Rock Hill. This sample was obtained from the Rock Hill 
pit at Tuckahoe, N. J., and is substantially the same as No. 6, 
except in having a greater per cent of voids and in containing some 
sandstone which crushes easily and materially reduces the voids 
of the gravel after it has been compacted in the road. It is said 
that the best results are obtained by mixing this and the preceding 
gravel half and half. 

8. Shark River. This gravel was obtained from the Manasquan 
Gravel Co. of Asbury Park, N. J., and is much used in southern 
New Jersey and around New York City. It consists wholly of 
clay and small rounded pebbles of pure white quartz, and conse- 
quently the only binding material is the clay and the 2 per cent 
of iron contained in it. 

9. Oaktown. This is a gravel obtained from the Wabash river 
by dredging, a few miles above Vincennes, Ind., which has been 
used on the roads entering Oaktown, Knox Co., Ind. There is 
very Httle clay in this gravel, — only 7.1 per cent, if the shale be 
considered as clay, as it is practically. The chief source of binding 
material is the 18.9 per cent of carbonate of lime, much of which 
is in the form of flat chips. The metamorphic rocks are also in 
thin chips, and are easily pulverized. The crystalline rocks and 
the quartz are comparatively rough and angular. In service the 
limestone pebbles grind up under traffic, and the road becomes 
hard and firm, and is not much affected by freezing and thawing. 

10. Shaker Prairie. This gravel is found in a pit on Shaker 
Prairie, west of Oaktown, Knox Co., Ind., and consohdates under 
traffic much more quickly than the preceding. This gravel contains 
a comparatively small amount of fine sand, being in this respect 



164 GRAVEL ROADS [CHAP. V 

about on a par with the Peekskill gravel — see No. 5, Table 24. 
It contains a comparatively large amount of clay, being in this respect 
similar to the New Jersey gravels — No. 7, 8, and 9 in Tables 24 
and 25. This gravel has more iron in the clay than any of the 
samples except the Tuckahoe gravels — No. 6 and 7. The limestone 
is in comparatively large rounded pebbles, and not easily crushed 
under traffic. The road is bound almost wholly by the clay and 
the iron in it, and by the pulverized limestone. 

11. Paducah. This gravel came from a pit about 2 miles west 
of Paducah, Ky., on the Ohio river at the mouth of the Tennessee 
river. It makes excellent roads that pack quickly under traffic 
and are not much affected by freezing and thawing. The coarse 
material consists of water-worn chert pebbles, and is cemented 
by ferruginous clay. The chert is brittle and crushes with a sharp 
splintery fracture, and consoHdates readily under traffic, the sharp 
angular fragments giving an immobile mass and offering excellent 
surfaces for the cementing action of the binder. 

12. Rosetta. This gravel comes from the Rosetta pit at Fort 
Gibson, near Vicksburg, Miss., and is much used by the Illinois 
Central Railroad as ballast. It is here included under the behef 
that it wiU also make good wagon roads. The quartz pebbles are 
quite rough and angular, and in the pit seem to be quite firmly 
cemented together by ferruginous clay. 

286. Conclusion. From the preceding, the following conclusions 
may be drawn. 1. The relation between the proportion of voids 
and the per cent of clay is no indication of the road-building qual- 
ities of a gravel, for under traffic some of the fragments may crush 
and decrease the per cent of voids and at the same time increase 
the amount of the binding material. 2. The friabifity of the pebbles 
has a greater effect upon the road-building quafities of a gravel 
than the per cent of the voids. 3. The binding material may be 
clay, or clay and iron, or pulverized limestone, or all of these com- 
bined. The less clay the more slowly will the road bind, but the 
less it will be affected by frost. 

A study similar to the preceding will not certainly determine 
the suitabiUty of a gravel for road purposes, but it wiU throw valu- 
able fight upon its probable behavior in the road. The only sure 
way to determine the road-building qualities of a gravel is to test 
it by actual service, for much depends upon the friability of the 
pebbles, the weight of the traffic, the climatic conditions, etc. In 
applying the test of actual service, particularly to determine the 



ART. 2] CONSTRtJCTroN 165 

relative merits of two gravels, account should be taken of (1) the 
nature of the soil, (2) the care employed in preparing the founda- 
tion, (3) the quantity of material used, (4) the amount and char- 
acter of the traffic, (5) the care given to maintaining the road, and 
(6) the length of time the material has been in service. The char- 
acter of a gravel road is generally indicated by the sound of the 
metal tires of the wheels of the vehicles passing over it. If the wheel 
makes a continuous crisp gritty sound, the road is reasonably good; 
if the gritty sound is absent, there is probably too much earthy 
matter on the surface; and if the sound is intermittent, there are 
probably too many large pebbles in the surface. 

Art. 2. Construction 

288. The subgrade for a gravel road should be prepared in sub- 
stantially the same manner as for an earth road (see Art. 1, Chapter 
III). Indeed a first-class earth road is the best foundation for a 
gravel road. 

289. Drainage. In no case should the drainage be neglected 
— neither the side ditches nor the underdrainage. With the hard, 
impervious surface of a gravel road, the water reaching the side 
ditches is greater than with an earth surface; and therefore the 
side ditches should be larger for gravel and broken-stone roads than 
for earth ones. 

A gravel road upon an undrained soil entails a needless expense 
for maintenance, and is never so good as if the road-bed had been 
thoroughly underdrained. Not infrequently a thin coating of 
gravel has been thrown upon an undrained foundation, only to 
sink out of sight in a year or two, and the attempt to secure a 
gravel road has been abandoned. In such cases a comparatively 
small expense for underdrainage would probably have resulted in a 
fair road instead of a failure. The total amount of good road-build- 
ing material in the world is small in comparison with the possible 
future demand, and therefore it is a public misfortune to have any of 
it wasted in bungling attempts at road building. One purpose of 
gravel is to give a more or less rigid layer which will distribute the 
concentrated pressure of the wheels over a sufficiently large area 
of the earth foundation to enable it to support the load without 
indentation. The thickness of gravel required to support the 
load depends upon the degree of the drainage, since the more water 
in the earth the less load it can support. Underdrainage costs 



166 GRAVEL ROADS [CHAP. V 

nothing for maintenance, and decreases the amount of gravel re- 
quired, as well as the cost of maintaining the surface. 

290. The tile should be placed under the side ditches — as de- 
scribed for earth roads (§ 116). Some writers recommend that a 
tile be laid under the middle of the gravel with the earth surface 
sloping both ways to the tile. There are several objections to 
this construction: (1) sloping the earth surface is not of much 
advantage, and (2) it needlessly increases the depth of the gravel; 
and (3) if the road is otherwise well made, the surface should be 
practically impervious to water. See § 124. 

Some writers advocate a tile each side of the graveled portion, 
with short Hnes of tile running each way from the center of the 
roadway obliquely to the side tile, these " miter drains " to be 
placed 15 feet apart in wet places. Clearly this construction is 
based upon a misapprehension of the source of the water reaching 
a drain tile. The water that enters a tile comes from below and 
not directly down from above. It is abundantly proven that in 
an earth road needing underdrainage, little or no water penetrates 
the surface; and with good gravel roads there will be still less. 
Therefore " miter underdrains " below the graveled portion of the 
roadway are absolutely worthless, and tiles at the edges of the hard- 
ened way are no better than tiles under the side ditches. 

291. Width. For a discussion of the principles governing the 
width of improved way and also whether it shall be located in the 
center or at one side of the wheel way, see § 95-98. For a consider- 
ation of the excess width on curves, see § 97. 

292. Maximum Grade. For a general discussion of maxi- 
mum grades, see § 79-86. A committee of the American Society 
of Civil Engineers recommends that the maximum grade permissible 
be 12 per cent — see Table 15, page 57. In the matter of permissible 
maximum grades, gravel and macadam roads are in the same class. 
For data concerning existing maximum grades on water-bound mac- 
adam roads, see § 112. 

293. Crown. The same general principles concerning the 
crown apply in gravel roads as in earth roads — see § 130-31. The 
slope of the gravel surface from the center to the side should be 
at least one quarter of an inch per foot, and it should not be more 
than three quarters of an inch per foot. The first is about right 
for park drives, which have hght traffic and are well cared for. If 
the drive is narrow, the crown may be a little greater than this; 
but if it is broad, the crown should be less, to prevent the surface 



ART. 2] CONSTRUCTION 167 

from being gullied out near the gutters by the water running from 
the center to the bides. The maximum crown, as above, would be 
about right for a country gravel road with heavy traffic, or for a 
street. If the gravel contains an excess of clay, the crown should 
be greater than the above maximum, as the surface will be liable 
to rut up. 

Frequently gravel roads have an excessive crown, which forces 
travel to use a narrow strip in the center — see § 129. This results 
from the fact that the gravel is placed thicker at the center than 
at the edges; and thus the surface of the gravel is given a greater 
crown than the original earth road, while a gravel road should have 
a less crown than an earth one. 

A committee of the American Society of Civil Engineers recom- 
mends a maximum crown of ] inch per foot of half width and a 
minimum of half that amount — see Table 16, page 65. 

294. For a rule for super-elevation on curves, see § 90. 

295. FORMS OF Construction. There are two forms of con- 
struction of country gravel roads, which differ as to the manner 
of preparing the subgrade to receive the gravel. In one form the 
gravel is simply deposited on the surface in a strip along the middle 
of the former earth road; and in the other a trench is excavated 
in which the gravel is placed. For convenience of reference the 
former will be called Surface Construction, and the latter Trench 
Construction. 

296. Surface Construction. The crudest form of this method 
of construction consists in dumping gravel, as it comes from the 
bank, in piles in line on an earth road. The quantity of gravel is 
gaged by dumping a load in one, or two, or three lengths of the 
wagon. Little or no attention is given to leveling off the top of 
the piles, and it is not rolled except as travel is forced upon the 
ridge when the earth upon the sides gets muddy. For the first year 
or two after construction, such a gravel road is little if any better 
than an earth one. The surface is full of cradle holes and is easily 
cut into ruts; and the loose material absorbs the rain, and be- 
comes mixed with the soil below. If the gravel is good, the road 
becomes fairly good after the gravel has been packed by travel and 
after the holes have been filled up by the addition of new material. 
This form of construction is common where gravel is plentiful, the 
work usually being done by labor road-tax. 

297. Another form of surface construction consists in setting 
up two lines of plank on edge and filUng the space between them 



168 



GKAVEL ROADS 



[chap. V 



with gravel. The gage planks are set en edge, 8, 10, or 12 feet 
apart according to the importance of the road, and the gravel is 
filled in between the planks, 8 or 10 inches deep at the sides and 
12 or 15 at the center. Of course, when the boards are moved 
forward to be used again, the edge of the gravel spreads out and 
takes the natural slope, and under traffic it spreads out still further. 
Ordinarily in this form of construction the gravel is not rolled, 
and there is Httle or no driving over it by teams engaged in the 
construction. The only advantage of this method over the pre- 
ceding one is that it affords a means of gaging the depth of gravel 
and of determining the quantity used; and the chief objection to 
it is that when gravel is put on in a thick layer, the lower part is 
not consoHdated well, at least not for a considerable time, and 
therefore the surface is liable to break up. This form of construc- 
tion is very common. 

298. In the best form of surface construction, the former earth 
road is first smoothed up with the scraping grader and if necessary 
the crown is reduced. If after smoothing the surface with the 
grader, the foundation is not already firm and solid, it should be 
rolled. Next a layer of gravel 4, or at most 6, inches deep is spread 
upon the prepared subgrade, and leveled — either by hand with a 
shovel and rake, or with a harrow or scraping grader. In dump- 
ing from a wagon or cart, the larger stones wiU roll to the outer 
edge of the heap; and hence in levehng the gravel care should 
be taken that these are scattered and covered deeply with fine 
material, for otherwise the road will not have an uniform texture 
and will wear unevenly and the large stones are Uable to work to 
the top. 

If the teams hauling the gravel are required to drive over that 
already placed, the road will be consolidated much sooner, but 
as the tractive resistance on loose gravel is very great, there is 
some disadvantage in this requirement. If it is to be insisted 
upon, the construction of the road should begin at the end nearest 
the gravel pit. The gravel can be consolidated with a roller, but not 
as effectively as by traffic, since no roller gives so great a pressure 
as the wheels of loaded wagons (see § 378). But heavy loads should 
not be permitted to go over the road while the surface is wet and 
soft, for fear the wheels will cut through and mix the earth and the 
gravel. While the gravel is being consolidated by the passage of 
the teams employed in the construction or by ordinary traffic, all 
ruts should be filled as soon as formed, by the use of a garden rake, 



ART. 2] 



CONSTRUCTION 



169 



and all saucer-like depressions should be filled by shoveling in fresh 
gravel. The cost of filling ruts and depressions will be more than 
saved in future repairs, and besides a much better road will be the 
result. 

After one layer has been thoroughly consolidated add a second, 
and so on until the desired depth is reached. The first layer may 
be the poorer gravel, the best being reserved for the top. All the 
layers should be added in time to get well packed before the rains 
and frosts of winter soften the road-bed. 

When finished the gravel should be deepest at the center and 
taper off to the sides. It is immaterial whether the first layer is 
the widest or the narrowest — there is a little advantage either way. 
The depth necessary will depend upon the nature of the soil, the 
quality of the gravel, the amount of travel, the maximum weight 
per wheel, and the care given to maintenance; but under ordinary 
conditions, a depth of 8 or 10 inches of compacted gravel at the 
center is sufficient. The width should vary with the amount of 
travel, but for a country road a depth of 6 inches at 4 or 5 feet 
from the center is sufficient. 

Fig. 43 shows the dimensions required in good practice. 




Fig. 43. — Cross Section op Gravel Road. Surface Construction. 



For data on the width of the actually traveled way on gravel 
roads, see § 95-96. 

299. Trench Construction. In this form of construction, a 
trench is excavated, 10 or 12 inches deep and of the required width 
for the reception of the gravel. The bottom of the trench is usually 
made parallel to the finished road surface by sloping it from the center 
toward the sides (see § 351). Fig. 44 shows the form when the 
finished surface is an arc. Fig. 44 is the standard form for state- 
aid roads in Connecticut, except that the width of the graveled way 
may be 12, 14, or 16 feet. The crown is | inch per foot of distance 
from side to center, or 6 inches for a 16-foot roadway. There is 
not much difference whether the road surface is an arc or two planes 
meeting in the center. The latter is probably a little the better for 



170 



GRAVEL ROADS 



[chap. 



country roads, although the former is the more common. Notice 
that in Fig. 44 the intersection of the road surface with the side slope 
of the embankment, is rounded off somewhat as recommended in 



U3ff.^\,3ff-JU. 



eft- 




>A^ bft -- 



TFT 



^^^ 2 in. layer \ 
3/r? layer \ 



Gnyi^fJ 



Half Section in Cut 



8/r?. 
Half Section in Pi 




Fig. 44. — Connecticut Gravel, Road. Trench Construction. 



Fig. 15 and 16, page 85. The exact method of rounding off the cor- 
ners in Fig. 44 is not specified. The thickness of the layers as shown 
is after consolidation. 

Fig. 45 shows the standard form of construction adopted by 
the Texas Highway Commission. Notice the wings in Fig. 45. 

The bottom of the trench should be rolled to consohdate it and 
to discover any soft places in the foundation. After rolling, any 
depressions should be filled and the foundation then re-rolled. The 
steam roller is better for this purpose than the horse roller, since it is 
heavier and since the horses' feet do not dig up the subgrade. For a 
discussion of rollers, see § 378. For precautions to be taken in roll- 
ing the subgrade, see § 369. 

A layer of 3 or 4, or at most 6, inches of gravel is placed in the 
trench, and the gravel is harrowed with a tooth harrow, and is then 
consolidated either by throwing the road open to travel or by rolling. 
The latter is preferable, since teams in passing each other are liable 
to break down the edges of the trench and mix the earth with the 
gravel, and since the wheels are liable to break through the thin 
layer of gravel — particularly if a wet time intervenes. If the only 




Fig. 45. — Texas Gravel Road. Trench Construction. 

gravel available contains an excess of large pebbles, they may be 
used in the lower layer, in which case the layer can not be compacted 
either by the wheels or by roUing. If the gravel is only sKghtly 



ART. 2] CONSTRUCTION 171 

deficient in binding material, it will be impossible to use a heavy 
roller, since the gravel will push along in front of it. 

Additional layers are added as rapidly as the preceding one is 
compacted, until the desired depth is reached. Before rolhng the 
last layer the earth at the sides of the trench, i. e., the " shoulders " 
or " wings," should be thoroughly rolled; and then the rolhng of the 
gravel should proceed from the sides toward the center, to prevent 
the gravel from slipping outward. The gravel will compact much 
better when damp; but if it is sprinkled, care should be taken that 
(1) the gravel is not made so wet that the earthy binding material 
becomes semi-fluid and collects on the surface, and (2) that the sub- 
grade is not unduly softened. 

No practical amount of rolhng will cause a gravel road to " come 
down " in the sense that a water-bound macadam road does; that 
is, a gravel road can not be rolled until the surface is as hard as it 
will probably be after it has been opened to traffic for a time, since 
even the heaviest rollers do not give as much pressure as the wheels 
of heavily loaded wagons. This difference between gravel and 
water-bound macadam roads is due to the fact that gravel has the 
binding material uniformly distributed throughout the mass, while 
with broken stone the binder is spread upon the top and worked in 
by rolling and sprinkling. 

300. Surface vs. Trench Construction. Surface construction 
is cheaper and seems to be much more common than trench con- 
struction. Surface construction is the better, since the depth of 
the gravel at different distances from the center is approximately 
proportional to the amount of traffic; while in the trench construc- 
tion, if the graveled portion is wide the sides are liable not to be much 
used, and if the graveled portion is narrow passing vehicles are 
forced upon the earth shoulders. Therefore it appears that surface 
construction is best for roads having a large amount of traffic. In 
park drives and streets, the whole width of the roadway is excavated 
and filled with gravel. 

Trench construction is a little more economical of gravel, and 
is therefore most suitable where gravel is expensive. 

301. Earth Road beside the Graveled Way. It is sometimes 
advocated that there should be two tracks, an earth road for sum- 
mer travel and a graveled way for winter use. This plan has some 
advantages and also some disadvantages. When the earth track 
is dry, it is preferred by most teamsters to the hard gravel road; 
and the use of the earth roadway decreases the wear on the gravel, 



172 



GRAVEL ROADS 



CHAP, V 



— which is clearly an advantage, for a gravel road like most other 
things will wear out. On the other hand, if the summer track 
is immediately adjacent to the hardened way, the earth of the 
former will become mixed with the gravel of the latter, much to 
the detriment of the gravel. The chief source of expense in the 
maintenance of gravel roads is due to the damage done by the 
mixing of earth from the side of the road with the gravel, thus 
forming a mixture that will hold water and cause the road to cut 
up. It has been suggested that the objection to the two tracks 
could be obviated by constructing a ditch, or sodding a narrow 
space between the two; but this is impracticable. The two tracks 
require a wider right-of-way, and therefore for this reason are fre- 
quently impossible. 

302. For a discussion as to whether the gravel road shall be in the 
center of the right-of-way or at one side, see § 98. 

303. BOTTOM Course. The gravel usually contains many 
stones too large to be used in or near the wearing surface, and 
therefore it is economy to screen the material and lay the larger 
pebbles in the bottom. Some writers object to using pebbles larger 
than 1 or 1 J inches in diameter for the bottom course, on the ground 
that the heaving effect of frost and the vibration due to the pass- 
ing wheels will cause the larger stones to rise to the surface and 
the smaller ones to descend — Hke the materials in a shaken sieve. 
Unquestionably, if a vehicle is driven over a layer of loose stones 
of all sizes, the larger ones will tilt up when the weight comes upon 
them and the smaller ones will roll down into the space made vacant 
by such tipping; and by a repetition of this process, the large stones 
will gradually reach the surface. The heaving action of the frost 
acts in a similar way. But it does not follow that a layer of coarse 
stones at the bottom of a gravel road will thus work to the top 
when the interstices of the gravel above are filled with binding mate- 
rial and all is compacted by traffic or by rolling. Experience has 
shown that if 2 to 4 inches of the top dressing has suitable binding 
material, it is extremely improbable that pebbles 2 to 2i inches in 
diameter in the bottom course will ever work to the surface. 

304. Other materials than coarse pebbles may be used for the 
lower course. In many locaUties there are large quantities of 
coal slack, which is useless as fuel and is too friable for the wearing 
surface of a road, but which can be used for the bottom course of 
a gravel road. Coal slack has thus been successfully employed, 
and is often cheaper than gravel. Blast-furnace slag has also been 



ART. 2] CONSTRUCTION 173 

used for this purpose. Sometimes broken stone is used for a bot- 
tom course; but on account of the expense of breaking, only a 
stone found already broken in the quarry is suitable for this pur- 
pose. A " flake " stone or quarry chips are the forms generally 
used. The celebrated gravel roads of Central Park^ New York 
City, have a '' rubble foundation " — not a Telford foundation 
(§ 349). The rubble layer is 10 to 12 inches thick, and the gravel 
4 to 6 inches after being thoroughly compacted. The stones, none of 
which exceeded 9 inches in greatest dimensions, were dumped upon 
the subgrade from carts and " evenly adjusted by a little labor 
of the hand.'' 

305. Screening the Gravel. As a rule gravel should be 
screened to exclude that which is too fine, and also to insure an 
even distribution of the fine and coarse material when placed upon 
the road. Where a small amount of gravel is required, the ordi- 
nary stationary incHned screen is used, the gravel being thrown 
against it with a shovel; but where a considerable amount is re- 
quired, it is much cheaper to use a rotary screen driven by power. 

If the gravel contains a considerable quantity of stones more 
than 2| or 3 inches in diameter, a stone crusher can be profitably 
employed, in which case it may be economical to use an elevator, 
rotary screen, and elevated storage bins, and to put all of the 
gravel through the crusher, rotary screen, and storage bin (see Fig. 62, 
page 205), 

Under favorable circumstances, the cost per cubic yard of screen- 
ing by hand will be about an hour's wages for a man for each time 
the material is handled with a shovel; while with the rotary screen, 
it can be screened to three sizes and be placed in elevated bins for the 
same amount. 

306. The Michigan State Highway Department, which builds 
many good gravel roads, requires the use of a rotary screen not less 
than 9 feet long and 30 inches in diameter, divided into three sec- 
tions having perforations 3, 2, and f inches in diameter. The 
Department divides road-building gravel into two classes as follows: 
The best contains at least 60 per cent of material passing a 2i-inch 
screen and caught on a |-inch screen; and the second class contains 
at least 40 per cent caught between these screens. The Department 
Hmits the clay binder to 10 per cent of the entire mass. 

The specifications of the American Society for Municipal Im- 
provements for 1916 divide mixtures of gravel, sand, and clay as 
foUows: No. 1 contains 60 to 75 per cent caught between the Ij-inch 



174 '^^^P GRAVEL ROADS [cHAP. V 

and the |-inch screen, and of this portion from 25 to 75 per cent 
shall be retained on the f-inch screen, and of the portion passing 
the J-inch screen from 65 to 85 per cent shall be retained on the 
200-mesh sieve. No. 2 contains 60 to 75 per cent caught between the 
2i-inch and the J-inch screen, and of this portion from 25 to 75 per 
cent shall be retained on the 1-inch screen, and of the portion passing 
the J-inch screen 65 to 85 per cent shall be retained on the 200-mesh 
sieve. No. 2 is to be used for the two lower courses of the road, and 
No. 1 for the top course. 

307. Hauling the Gravel. Gravel is usually obtained from 
pits, and is generally overlaid with more or less earth, which should 
be entirely removed before beginning to haul the gravel. Not infre- 
quently this earthy material is allowed to tumble into the pit and 
mix with the gravel, greatly to the detriment of the finished road. 

The loading of the gravel can be greatly facilitated by using a 
board platform 8 to 10 feet long and 4 to 6 feet wide. This plat- 
form is placed against the bottom of the bank in such a manner 
that when the gravel above is dislodged it falls upon the platform, 
from which it is easily shoveled into the wagon. Often the plat- 
form can be supported upon legs at a height above the top of the 
wagon, and the gravel can be simply pushed off into the wagon 
with the shovel. Sometimes the circumstances justify the use 
of a drag scraper (§ 150) — drawn by a horse attached to a cable 
passing through a block — to drag the gravel to the edge of the plat- 
form, whence it drops into the wagon; and sometimes, if a large 
quantity is to be loaded and a large number of teams are engaged 
in the hauling, the wagons can be loaded with a trap — an elevated 
platform upon which the gravel is hauled with a drag or a wheel 
scraper, and through which it drops into the wagon below. 

308. Measuring the Gravel. When gravel roads are built 
by public officials, the gravel is usually measured in the pit or in 
the wagon. The former is the better practice, since it is more definite. 
When the road is built by contract, the gravel is measured (1) in 
the wagons, or (2) loose in the road by means of gage boards, or (3) 
compacted in the road by means of established grades. The first 
or second method is generally used with surface construction, and the 
third with trench construction. With the last, it is customary to 
require that the finished surface shall conform to an estabHshed grade; 
and consequently a considerable quantity of gravel is hable to be 
forced into the subgrade, — particularly if the earth foundation is 
made to conform to the grade established for it. The specifications 



ART. 2] CONSTRUCTION 175 

for state-aid roads in New Jersey specify that " the contractor is to 
place sufficient gravel on the road to allow it to shrink 33 per cent 
in roUing and settling." Loose gravel with clay or loam binder will 
shrink 12 to 15 per cent in rolling, and gravel in which the binder is 
produced by crushing part of the material will shrink still more — 
possibly twice as much; the above specifications provide, therefore, 
for the possibility of forcing 18 to 21 per cent of the gravel into the 
subgrade. 

If it is expected that part of the gravel may be forced into the 
soil, the subgrade may be left a little higher than the established 
grade; and then the addition of the stipulated amount of gravel will 
bring the finished surface to the specified grade. Or, a thin layer 
of sand on the subgrade will sometimes prevent the gravel from 
being forced into the soil. For a further discussion of this subject, 
see § 377. 

309. Cost. The cost of gravel roads varies greatly with the 
form of construction, the cost of gravel, the amount of grading and 
drainage required, the width and thickness of the gravel, etc. An 
average depth of 1 foot over a width of 13J feet requires half a 
cubic yard per linear foot of road, or 2,640 cubic yards per mile. 
The gravel usually costs from 5 to 10 cents per cubic yard stripped 
in the bank. The cost of loading will vary from 5 to 10 cents per 
cubic yard, not including the time lost by the team in waiting for 
a load. Setting gage plank, leveling, etc., may cost from 2 to 10 
cents per cubic yard. The cost of hauhng varies materially with 
the time of year (see § 4), and including the time lost in loading 
and unloading, will usually be at least 15 cents per cubic yard 
(about IJ tons) per mile and seldom more than 30 cents — the 
former when done by farmers in the slack season and the latter 
when done by teamsters. For a haul of 1 mile the total cost in 
place is 40 to 50 cents per cubic yard. 

310. Reports from forty-four counties in Indiana show that the 
total cost of construction of gravel roads in that state varies from 
$800 to $3,500 per mile; and except in a few counties, the cost 
varies from $1,000 to $2,500, and is generally from $1,000 to $2,000. 
The cost varies with the distance about as follows: when the gravel 
is hauled 1 mile, the total cost of the road is $1,000 per mile; when 
the haul is 2 miles, $1,250 per mile; when the haul is 3 miles, $1,500 
per mile; when the haul is 4 miles, $1,750 per mile; and if 5 miles, 
$2,000 per mile. Numerous data from Ohio and Illinois seem to 
show that the above prices are fairly representative. 



176 GRAVEL ROADS [CHAP. V 

In Missouri in 1912 one-course gravel roads 10 feet wide cost 
$800 to $1,800 per mile, and 15 feet wide from $1,500 to $2,500, 
exclusive of grading, drainage, culverts, interest, and profits. 

In Michigan in 1913 the average cost of 68 miles of state-aid 
gravel roads was as follows: 

Items. ' Average Cost 

Per Mile. Per Sq. Yd. 

Shaping and draining $455.46 $0,086 

Gravel, loading and hauling, 1,649 cu. yd 247 . 34 . 046 

Culverts, etc 71.93 0.013 

Surfacing 1 661.85 0.316 

Total $2 436.58 $0,460 

311. Economic Value of a Gravel Surface. The value 
to a community of covering an earth road with gravel is a subject 
the discussion of which leads different persons to widely different 
conclusions, depending upon the point of view and upon the data 
assumed. 

The advantage of a gravel surface over one of earth is that the 
hard and impermeable surface of the former is equally good at all 
seasons of the year. The financial value of a road which is good at all 
seasons of the year varies greatly with the locality and the occupa- 
tion of those who use it. Near a large city such roads are nearly 
indispensable to dairymen, fruit growers, and truck farmers; but 
permanently hard roads are not of great financial advantage to 
grain growers and stock raisers, except in the immediate vicinity 
of a large city. A road which is uniformly good at aU seasons of 
the year is of some economic advantage to a farming commimity, 
since it permits hauhng to be done at times when other work is 
impossible, and since it makes possible the marketing of commodi- 
ties when the price is most favorable. It is impossible to compute 
the money value of these factors; but, in general, it is not very 
great (see § 4-7). The chief advantage of a road good at all seasons 
of the year is its effect upon the social life of the rural district 

(§ 1-3). 

The amount of a load than can be hauled on an earth road is 
often determined by the grades rather than by the nature of the 
surface; and unless the grades are light, the maximum load for a 
gravel road is not much greater than that for a dry earth road. 
Therefore, before adding a gravel surface to an earth road, the 
gradients should be carefully studied with a view of deriving the 



ART. 2] 



CONSTRUCTION 



177 



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178 GRAVEL ROADS [CHAP. V 

utmost benefit of the improved surface by securing easy ruling 
grades (see § 74). 

312. The cost of the improvement is the sum of (1) the annual 
interest on the cost of construction, (2) the excess of the annual cost 
of maintaining the gravel road over that of maintaining the earth 
road, and (3) the annual payment necessary to accimiulate a fund 
sufficient to make periodic repairs, i. e., to add a new surface at 
intervals. The money spent in road improvements is to be con- 
sidered as an investment which will return annual interest in the 
reduced cost of transportation and in the greater freedom of traffic 
and social intercourse. 

313. Durability. On account of the low first cost of the gravel, 
and the fact that reasonably good gravel roads can be built without 
any investment of money in rollers, crushers, and other costly 
machinery, they are well suited to light traffic roads, to residence 
streets in small cities, and to park drives. A gravel road well built 
of good material is excellent for automobiles, and will safely carry 
a considerable number daily — see Table 26, page 177. 

314. Specifications. The American Society of Municipal 
Improvements publishes standard specifications for the material 
and workmanship of gravel roads. The specifications are modified 
from time to time as is necessary to keep them up to date. Printed 
copies may be had of the secretary for a nominal sum. 

The various State Highway Departments also publish standard 
specifications 

Art. 3. Maintenance 

316. There are more miles of gravel roads in this country than 
of any other type of improved roads; and therefore the proper main- 
tenance of these roads is an important matter. If properly con- 
structed and reasonably maintained, a gravel road is quite satisfac- 
tory except under very heavy travel. 

The proper care of side ditches, culverts, shoulders, and the 
surface has been considered in the discussion on earth roads — 
Art. 2, Chapter III ; — and all that has been said there applies equally 
well to gravel roads. The maintenance of a gravel road is more im- 
portant than that of an earth road, because more is rightly expected 
of the former than of the latter ; and since the gravel road represents 
a greater investment, neglect may result in greater damage. 

317. Destructive Agents. The destructive agents are the 
same for gravel as for earth roads (see § 198-204), except that for 



ART. 3] MAINTENANCE 179 

gravel roads a gradient is an element of destruction whose impor- 
tance varies with its steepness. Horses in drawing a load up a hill 
or in holding back a load in coming down, are liable to displace 
pebbles with the calks of their shoes, and after the first stone is 
displaced it is easier to loosen others. The locking of the wheel, 
until it slides in going down hill, is also hard on a gravel road. 

Grades have a further disadvantage. Automobiles are likely 
to speed up at the bottom of the grade so as to reach the top at a 
fair velocity, and the sudden acceleration of the speed is likely to 
dislodge pebbles and cause the road to ravel. 

318. THE Method of Maintenance. The three methods of 
maintenance employed in caring for earth roads (§ 222-26) are also 
employed for gravel roads. Since gravel roads represent a greater 
investment, and since more is expected of them, it is desirable that 
they shall be cared for under the patrol system, that is, the system 
of continuous maintenance. 

When a gravel road is first thrown open to traffic, it should be 
carefully watched and all incipient ruts and depression should be 
filled as soon as formed, either by raking in gravel from the sides of 
the depression or by adding fresh gravel — ^in the earlier stages of this 
work the former is the better, and in the later stages the latter is 
necessary. The new gravel should be finer and contain more bind- 
ing material than that employed in the original construction. If the 
depression is very shallow, it is wise to roughen the surface with a 
garden rake before adding the new material. It is important that 
ruts and shallow holes should be filled as soon as they appear, 
for they will hold water, which will soften the gravel bed and cause 
the road to wear rapidly. At, say, every | mile a small pile of gravel 
should be stored to be used in filling depressions. 

If the road surface becomes muddy when wet, there is an excess 
of clay binder ; and therefore a thin layer of coarse clean sand or fine 
clean gravel, preferably the latter, should be added. On the other 
hand, if the surface shows a tendency to disintegrate or ravel, there 
is not enough binder; and therefore a layer of clay should be added 
and harrowed into the gravel. However, if the surface does not at 
once set up, it should not be concluded that there is not enough 
binder, for a road that binds quickly is likely to cut up badly, par- 
ticularly when wet. 

During this stage, all loose stones should be removed from the 
roadway, both for the comfort of travelers and the good of the road. 

After the gravel has become thoroughly consolidated, i. e., after 



180 GRAVEL ROADS [CHAP. V 

the wheels no longer make even shallow ruts, the only care the 
road is likely to need for several years is to keep the side 
ditches and culverts free from weeds and floating trash, and to 
attend to the drainage of the surface when the snow is melting 
(§219). 

After a time the gravel will work out to the sides of the road too 
far, and the center wiU wear hollow. It will then be necessary to use 
a scraping grader (§ 155-56) to push the gravel back to the center. 
In doing this care should be taken not to scrape up the earth with the 
gravel. A good time to use the grader is just after a rain, when the 
road is soft and easily scraped, and when the gravel scraped to the 
center is in the best condition to pack again. The road should never 
be allowed to wear so hollow in the center as to interfere with the flow 
of water from the surface to the side ditches. 

319. Sprinkling. A gravel road with clay binder needs a httle 
moisture to hold it together, since the clay shrinks and cracks under 
excessive drought, loses its binding power, and permits the road to 
break to pieces. Under such circumstances a sprinkling with water 
is a means of preserving the road from serious damage, although 
on account of the expense this is seldom done except on park 
drives. 

320. Re-Surfacing. It will finally be necessary to repair the 
surface by adding a coating of new gravel. For this purpose the size 
of the largest pebbles should vary with the thickness of the coat. It is 
usual to put the gravel on by making two or three dumps of a wagon 
load, i. e., by stretching a cubic yard over 15 to 25 linear feet, accord- 
ing to the thickness of layer required, and spreading the gravel just a 
little wider than the wagon track. Traffic will spread it still wider, 
and also pack it. 

In making repairs, it is better to apply a thin coat often than a 
thicker coat less frequently, since a thick coating does not pack 
well. A layer of 2 inches of gravel is better than more — unless on a 
spot that has cut through. 

321. Cost. The cost of maintenance varies with the climate, 
the amount and nature of the traffic, the quality of the gravel, etc. 
Data from Indiana and Ohio show that it varies from $40 to $100 
per mile per annum — ^the former where the traffic is light, the gravel 
good, and the snow light; and the latter where the traffic is heavy, 
the gravel poor, and the snow heavj^ In New Hampshire the cost 
is $20 to $100, usually, $20 to $50 per mile per year exclusive of re- 
surfacing; or including re-surfacing, $150 to $300 per mile per year 



ART. 4] DUST PALLIATIVES 181 

for all expense.* In Vermont the average cost of maintaining 175 
miles in 1912 varied from $10.97 to $32.33, the average being $20.71. 

Art. 4. Dust Palliatives 

323. The surfaces of gravel roads are treated for two distinct 
pm'poses, — to lay the dust and to bind the surface materials. The 
agents that accomplish the first are called dust palliatives; and 
those that secure the second are called road binders, protective 
coatings, or bituminous carpets. Only the first will be considered 
here. 

324. DUST PREVENTIVES. The suppression of the dust from 
an earth road is in the interests of the people using the road or re- 
siding adjacent to it; but the prevention of dust on a gravel road is 
important not only to the interests of those using the road or living 
near it, but also to the very life of the road itself. The simplest 
materials used for this purpose are: Fresh water, salt water, deli- 
quescent salts, proprietary compounds, oil, and tar. The two latter 
are the most common, and are used primarily as road binders, al- 
though they incidentally prevent the binder of the gravel from being 
blown away as dust. 

325. Sprinkling with Fresh Water. This is the simplest method 
of preventing dust. Sprinkling a gravel road with water not only 
suppresses the dust, but prevents the disintegration of the surface by 
raveling (see § 397). The water should be applied in a fine spray, 
and in such quantities as not to run in streams on the surface; that 
is, several light sprinklings are better than a single flooding. If 
sprinkled too heavily or too often, the road is softened and breaks 
up easily. 

Reliable and definite data concerning the cost of sprinkling are 
rather meager. Dust may usually be kept down on a gravel road 
carrying a moderate amount of heavy travel, by sprinkling, for about 
2 to 3 cents per square yard per annum. 

326. Sprinkling with Sea Water. This is a simple remedy, but 
obviously is applicable only to roads located near the sea coast. Sea 
water is more effective in laying dust than fresh water owing to cer- 



* From an instructive account of the patrol system of maintenance employed by the New 
Hampshire Highway Department, in Engineering News, Vol. 74 (1915), p. 1110. For an 
orticle explaining the use of gasoline motor trucks and trailers in maintaining gravel roads in 
Alabama and giving data on the cost of the work, see Engineering Record, Vol. 74 (191C), p, 
73-74. 



182 GRAVEL ROADS [CHAP. V 

tain deliquescent salts which it contains; but the presence in the 
sea water of salts not possessing hygroscopic properties causes disa- 
greeable and destructive mud in wet weather, and renders this form 
of treatment rather unsatisfactory. 

327. Moistening with Deliquescent Salts. Solutions of water 
and various deliquescent salts have been used to moisten the surface 
of roads to prevent dust. The effect of these solutions is more lasting 
than that of fresh water alone, and they are easily applied by the 
ordinary sprinkling wagon. However, some difficulty is encoun- 
tered in obtaining a solution of constant strength, and its cost is 
considerable. 

Among the most common of these salts is calcium chloride, 
which may be obtained commercially in a granular condition or in a 
concentrated solution. The granular salt may be applied with an 
ordinary agricultural drill. When applied in granular form about 
three fourths of a pound per square yard is used for the first applica- 
tion, and slightly less for succeeding ones. When applied in liquid 
form, a 15 per cent solution is ordinarily used for the first application, 
and for successive applications an 8 or 10 per cent solution is em- 
ployed. Of course, such salts are not suitable in arid or semi-arid 
regions, since there is but little moisture in the air to be absorbed; 
nor in an extremely humid climate, since the salt is likely to be 
washed away by the rains. Calcium chloride is odorless and clean, 
but has no permanent effects upon the road. It may cause soreness in 
horses' feet, if used in quantities much in excess of those stated above. 

328. Sprinkling with Proprietary Compounds. There are a 
number of proprietary dust-laying compounds upon the market. 
Most of them consist of deliquescent salts dissolved in water, and 
some consist of by-products from manufacturing. The names of a 
few of the first class are: Aconia, calcite, and panscale. Several of 
them seem to be no more efficient than calcium chloride, but are con- 
siderably more expensive. 

329. Sprinkling with Light Oil. The dust of a gravel road may 
be laid by sprinkling it with oil much as was described for an earth 
road (§ 236-39); but it is usually more economical to apply a pro- 
tective coating or bituminous carpet (Art. 1 and 2 of Chapter IX) 
which not only prevents to a certain degree the formation of dust, 
but protects the surface of the road. 

Oil as a dust layer was used chiefiy on park drives and suburban 
roads, but has been abandoned where there is any considerable 
amount of automobile travel. The following account from the pre- 



ART. 4] DtJST PALLIATIVES l83 

vious edition of this volume describes the former practice in Wash- 
ington, D. C. 

330. Practice in Washington, D. C. The city of Washington, 
D. C, formerly sprinkled the gravel park drives with the light as- 
phaltic oil described in § 552. The following is a description of the 
method then employed in applying the oil.* 

" All ruts and holes in the surface of the road are first repaired 
by cleaning out the cavity, filling it with coarse stone which is cov- 
ered with a coating of hot, heavy, asphaltic oil, then sprinkling a 
light coat of screenings over the oil, and finally compacting the 
patch by ramming. When all holes have been thus repaired, the 
surface of the road is thoroughly cleaned with rattan brooms, care 
being taken to remove all loose materials and caked dirt or dust so 
that the stone forming the wearing surface of the road shall be 
exposed and clean. 

'' When the road is entirely free from moisture, and during warm 
dry weather, if possible, a hght asphaltic oil is spread (without being 
heated) by means of special sprinkling wagons. One third to one 
half gallon of oil to the square yard usually forms the first applica- 
tion. To allow it to penetrate into the surface, the road is closed to 
traffic at least 48 hours after the first application. 

"At the end of this time the surface of the road is covered with 
a thin coating of clean, coarse, sharp sand or stone screenings, free 
from dust; and is then rolled and traffic allowed to go over it. A 
cubic yard of sand or screenings usually covers from 75 to 125 square 
yards of road surface. 

^' The oiling described above keeps the surface in excellent con- 
dition for a year. It is never dusty, and is muddy for only a few 
hours after a heavy thaw when the skid-chains of automobiles tear 
up the surface. The subsequent passage of automobiles without 
chains soon irons out the roadway. At the end of the year the sur- 
face of the road is again thoroughly cleaned, from ^ to J gallon of oil 
to the square yard under normal conditions being spread over it, and 
the road closed for 48 hours and covered with sand or screenings 
as before. This treatment is continued from year to year." 

" The cost, for the first application, from 2.8 to 4.6 cents per 
square yard; and for the second application from 1.3 to 2.8 cents per 
square yard." 

* Paper by Col. Spencer Cosby, U. S. Army, in Charge of Buildings and Grounds, Wash- 
ington, D. C, presented before Section D^of the American Association for the Advancement 
of Science, on Dec. 29, 1911. 



184 



GRAVEL ROADS 



[chap. V 



331. The amount of oil applied is often considerably greater than 
that employed in Washington, D. C, as mentioned above, being 
from 0.3 to 0.4 gallon per square yard, in which case the total cost of 
material and labor is from 4.0 to 7.0 cents per square yard. When 
the quantity:required is as great as this, it is probable that the ex- 
pense is not justifiable, since instead of spending the larger sum for a 
light oil, it is more economical to spend a little greater amount for 
a heavier oil or for a stronger binding material, and construct a more 
durable protective coating (see § 583). 



CHAPTER VI> _^ 

WATER-BOUND MACADAM ROADS 

334. Throughout the entire nineteenth century a road built 
by placing small fragments of broken stone on the ground and com- 
pacting them into a solid mass by roUing or by travel was called a 
macadam road, after John Loudon MacAdam (1756-1836), a famous 
EngUsh builder of broken-stone roads and one of the first to build 
such roads. The broken stone is called macadam, and the work of 
construction macadamizing. 

A broken-stone road is sometimes called a telford road after 
Thomas Telford (1757-1834), a famous English engineer; but the 
term telford is usually, and appropriately, restricted to a particular 
form of the foundation of a broken-stone road (§ 349). 

The fragments of stone in the road referred to above were held 
together by the cementing power of the dust of the stone; but the 
use of the automobile has shown the desirabihty of a broken-stone 
road having a binder stronger than stone dust; and this led in the 
early years of the twentieth century to the introduction of a new 
type of broken-stone road — one bound with a bituminous cement, such 
as tar or asphalt. Such a road is called a bituminous madacam road; 
and consequently the broken-stone road having a stone-dust binder 
is now called a water-bound macadam road. 

For more than a hundred years the water-bound macadam was a 
leading form of improved road all over the world, and even now it 
is exceeded in mileage only by^ earth and gravel roads; but, since the 
early years of this century, it is much less frequently built than 
formerly. It is used now only in rural roads having comparatively 
little motor-driven travel and on residence streets having but little 
through travel. In some particulars the water-bound macadam 
road will be discussed a little more fully than its individual merits 
may warrant, because many of the principles of its construction are 
appHcable to bituminous roads, which are becoming increasingly 
important. 

185 



186 WATER-BOUND MACADAM ROADS [CHAP. Vl' 



Art. 1. The Stone 

335. Requisites for Road Stone. The principal requisites 
of a material for a water-bound macadam road are hardness, tough- 
ness, cementing or binding power, and resistance to the weather. 
Usually any stone that is hard and tough will resist the weather 
reasonably well; but shales and slates, though hard and tough when 
first quarried, often disintegrate when exposed to the weather. 
The material for a road surface should also be uniform in quality 
or the surface will wear unevenly; and the depressions which occur 
where the material is comparatively soft will hold water, thus soften- 
ing the road-bed and occasioning damage difficult to repair. 

336. Hardness and Toughness. These two qualities are closely 
related. Hardness is that property of a soUd which renders it dif- 
ficult to displace its parts among themselves; while toughness 
enables the parts to yield somewhat without being separated or 
broken. For road purposes, hardness is the power possessed by 
a rock to resist the rubbing or the abrasive action of wheels and 
horses' feet; while toughness is the adhesion between particles of 
a rock which gives it power to resist fracture when subjected to 
blows. A stone may be hard and brittle, and be quickly pounded to 
pieces in the road, as quartz; or it rray ha\e a high crushing strength 
and yet be deficient in toughness, and grind away speedily under the 
abrasion of traffic, as some varieties of sandstones. A road metal 
should have enough resistance to crushing to support the load brought 
upon it by the wheels, and enough toughness to prevent its being 
readily ground into powder. A large part of the fine material is 
inevitably swept away by the rains and winds, or is removed by 
scrapers to keep the road in good condition during wet weather; 
and therefore it is important that the fragments should be tough 
enough not to be unduly pulverized by travel. Toughness is incom- 
patible with a high degree of hardness, and in a measure makes up 
for a deficiency in resistance to crushing. Hardness could be meas- 
ured by the resistance offered by a rock to the grinding of an emery 
wheel; and toughness would be measured by the resistance to frac- 
ture when struck with a hammer. 

337. Cementing or Binding Power. Binding power is the prop- 
erty possessed by rock dust to act as a cement between the coarser 
fragments composing a stone road. This property is of the highest 
value, for the strength of the binder determines the resistance of the 



A.RT. 1] THE STONE 187 

road to the wear and tear of travel more than does the strength of 
the fragments themselves. It is possessed in a very much higher 
degree by some varieties of rocks than by others, and its absence is 
so pronounced in some varieties that they can not be made to com- 
pact under the roller or under traffic without the addition of some 
cementing agent. 

338. Methods of Testing Stone. There are two methods 
of determining the qualities of a stone for road-building purposes: 
(1) by using the stone in the road and keeping an account of the 
cost of repairs over a series of years, or (2) by laboratory experi- 
ments. The first is uncertain owing to the variations in climatic 
conditions, and in the amount and nature of the traffic, etc.; and 
would be very expensive and take a long time. In the second 
method of testing, it is difficult to duplicate in the laboratory the 
conditions of actual service; but nevertheless much valuable infor- 
mation may thus be obtained at a moderate expense and in a com- 
paratively short time. 

Systematic laboratory tests of road metal are of comparatively 
recent origin, and may be said to have been started about 1880 by 
the French governmental engineers, who have made extensive use 
of this method in determining the quality of the rock used in con- 
tract work and in selecting new quarries. Only a little such labora- 
tory work has been done in England and Germany. From 1894 to 
1899 the Massachusetts Highway Commission conducted a series of 
tests of road-making materials, and developed new and important 
methods of testing, and deduced much valuable information. 

339. Since the latter date the U. S. Office of Pubfic Roads and 
Rural Engineering has conducted extensive laboratory tests of the 
road-building stones. Bulletin No. 370 (1916) describes the methods 
employed and gives the results obtained for 3,650 samples from forty 
states and three foreign countries. The Laboratory tests road 
materials for public officials without cost; and also gives advice as to 
the value of the material for road-building purposes. 

340. The principal tests applied to stone for water-bound mac- 
adam roads will be very briefly described. 

341. Hardness Test. This test determines the hardness of the 
stone; and virtually consists in measuring the amount ground off 
under certain conditions. The loss in the above tests varied from 
1.0 to 32.8 per cent, usually from 2 to 10. The test is made with the 
Dorry machine. 

342. Toughness Test. This test is to determine the resistance to 



188 



WATER-BOUND MACADAM ROADS 



[chap. VI 



impact. It is made by finding the number of hammer-like blows 
required to break a cylindrical specimen. The results range from 3 
to 43, about half of the materials requiring from 10 to 20 blows. 
The test is made with the Page impact machine. 

343. Abrasion Test. The results of this test depend upon both 
hardness and the resistance to abrasion. Fragments of the stone are 
rotated in a cylinder inclined to the axis of rotation, and the amount 
worn off is determined. The result is expressed either in per cent of 
wear or in the arbitrary French coefficient of wear, which equals 
40 divided by the per cent of wear. The latter is in more common 
use. The French coefficient of wear for the test referred to in § 339 
ranges from 1.4 to 41.7, usually from 10 to 30. The test is made with 
a Deval machine. 

344. Cementation Test. This test determines the binding power 
or cementing value of the stone dust to hold together the coarser 
fragments of a water-bound macadam road. This is the most 
important quality of a stone for such a road. The test is made by 
placing small fragments of stone and water in a ball mill and grinding 
them to a stiff paste, which is then moulded into a briquette under 
heavy pressure. The briquette is dried and tested in an impact 
machine to determine the number of blows required to break it. 
The results range from to over 500. Values below 10 are called 
low; from 10 to 25, fair; from 25 to 75, good; from 75 to 100, very 
good; and above 100, excellent. The results for a few stones are as 
follows: 



Name. 


Max. 


MiN. 


Name. 


Max. 


MiN. 


Andesite 


500+ 

500+ 

500 + 

500 + 

500+ 

148 

255 


9 
2 
2 
20 
2 
5 
2 


Gravel 


500 
500 

85 

45 
500 + 
367 
500+ 


3 


Basalt 


Limestone 


9 


Chert. 


Marble 

Quartzite 


10 


Conglomerate. 





Diabase .... 


Sandstone 


1 


Diorite. 


Shale 


28 


Granite 


Slate 


1 









345. Conclusion. The principal rocks used for water-bound 
macadam roads are traps (a popular term which includes diabase, 
diorite, and several other igneous rocks), granites, and limestones. 
Their value for road-building purposes is in the order named. In 
the Eastern States the traps are the ones most used, in the Missis- 
sippi Valley limestone is the most common. 

For information concerning the road-building materials of the 



ART. 2] CONSTRUCTION 189 

United States, see Preliminary Report on the Geology of the Common 
Roads of the United States, by Nathaniel Southgate Shaler, in U. S. 
Geological Survey, Fifteenth Annual Report, 1893-94, p. 255-306. 

Art. 2. Construction 

347. The principles of construction for earth roads apply also to 
the construction of the subgrade for broken-stone roads (see Art. 
1, Chapter III). The drainage of the foundation by tile drains and 
side ditches should not be neglected (see § 114-24 and § 125-28). 

348. FORMS OF Construction. With reference to the method 
of preparing the subgrade to receive the stone, there are two forms 
of construction — surface construction and trench construction. The 
surface construction consists simply in placing a layer of broken 
stone upon the earth road and leaving it to be compacted by travel. 
In the West many miles of road are constructed on this plan with 
limestone. As a rule this material readily pulverizes under the 
traffic, and the powder cements well; consequently the road soon 
binds together. Such roads are not first class, but they give good 
returns on their cost. On account of the simplicity of the con- 
struction, this form will not be considered further. 

The trench construction consists in excavating a trench of the 
required width and depth, and depositing the broken stone in it. 

349. With reference to the lower course of stone there are two 
systems of construction, — the macadam and the telford (§ 334), 
The macadam road consists of two or more layers of crushed stone, 
its distinguishing characteristic being that the lower course of crushed 
stone is placed directly upon the earth road-bed. The telford road 
consists of a foundation or pavement of rough stone blocks set upon 
the road-bed, covered with one or more layers of crushed stone, the 
distinguishing feature being the paved foundation. 

350. Telford vs. Macadam Roads. Each of these systems has 
its earnest advocates who contend for its exclusive use. 

The most important claims of the advocates of the telford con- 
struction are (1) that the open foundation is necessary for drainage; 
(2) that the sub-pavement is necessary on soft or poorly drained soil 
to prevent the small fragments of broken stone from working down 
into the soil and the soil from working up into the stone; and (3) 
that the telford is the cheaper, since the expense of crushing is saved. 

The most important claims of the advocates of the macadam 
system are: (1) that the drainage afforded by the telford construe- 



190 



WATER-BOUND MACADAM ROADS 



CHAP. VI 



tion is no better than that with the macadam construction; (2) 
that on any well drained soil there is no tendency of the stone to 
work down or of the soil to work up; (3) that tile drainage and 
macadam construction are cheaper than the telford system; and 
(4) that since the introduction of the machine rock-breaker, it is 
cheaper to crush the stone and lay the macadam foundation than 
to place the telford. 

The view taken by different road builders in this matter is prob- 
ably largely due to the conditions in the vicinity in which they have 
worked and to the skill with which the two systems have been applied 
in work which has come under their observation. The foundation 
which is proper in a given case is determined by the nature and con- 
dition of the soil upon which it is constructed. If the road-bed is 
thoroughly drained and is composed of material which will not readily 
soften, there will be no need of a telford foundation. If, on the other 
hand, the soil is retentive of moisture and can not be thoroughly 
drained, it may be necessary to provide a foundation which will 
prevent the soil from working up into the stone and the road metal 
from working down into the soil. 

To MacAdam is due the credit of discovering the supporting 
power of a layer of comparatively small angular fragments of stone. 

351. Forms of the Subgrade. The finished surface of the road 
should have sufficient crown to shed the rain water into the side 
ditches. There are in common use two methods of securing this 
crown. In one the earth surface is made level, and the slope is given 
by a greater thickness of metaling at the center than at the sides ; in 
the other, the slope or camber is given to the earth bed, and the metal 
has a uniform thickness. The advocates of the first system say that 
there is more wear at the center than at the sides, and that conse- 
quently the metaling should be thicker at the center. Those in 
favor of the uniform thickness say that as the pressure on the earth 
is practically the same at the sides as at the center, the thickness 
should be uniform, since the principal object of the layer of stone 
is to distribute the concentrated pressure of the wheel over a greater 
surface of the earth bed. Both forms of construction are in common 
use, although the preference seems to be slightly in favor of making 
the subgrade parallel to the finished road-surface and the stone of 
uniform thickness. A level subgrade is slightly cheaper to form. 

Fig. 46 shows a cross section of the celebrated Shrewsbury 
and Holyhead road in the west of England, built by Telford 
in 1815. The construction of this road, which formed a link in 



ART. 2] 



CONSTRTJCTIOJg' 



101 



the direct line of communication between England and Ireland, 
was made a national undertaking, and resulted in what was at that 



^--6/7 ->*< /art ' J 



•H — err---^ ^. 
Uin. 'A 



Fig. 46. — Telford's Shrewsbury and Holyhead Road. 

time one of the finest pieces of road construction in the world. Notice 
that the subgrade is flat. 

Fig. 47 shows a modern telford road as built in New Jersey. 



K--- 7ft >»< I4^ft 

I ' 



— K — yrr 




Fig. 47. — Modern Telford Road as Built in New Jersey. 

Notice that the base of the foundation is parallel to the surface of 
the finished road. 

Compare the above with Fig. 51-56, pages 197-99. 

352. Width. For a discussion of the principles governing the 
the width of the improved way, and silso whether it shall be in the 
center or at the side of the wheelway, see § 95-98. 

353. Shoulders. The discussion referred to above deals only 
with the width of the paved portion; but there should be an addi- 
tional width of earth sufficient to keep the broken stone in place, 
particularly while being rolled. This strip of earth is usually called 
a shoulder, but sometimes and improperly a wing (see § 364). The 
proper width of the shoulder will depend upon the soil, the climate, 
and the amount of rolling it receives. Usually 2 or 3 feet is suf- 
ficient, although 5 to 7 feet is frequently provided — see Fig. 47. 
The Swiss road shown in Fig. 53, page 198, has a shoulder of only 18 
inches. An excessive width of shoulder adds greatly to the cost of the 
road when in excavation or on embankment. The surface of the 
shoulder should conform to the general curve of the finished road- 
way. The shoulder serves the double purpose of holding the broken 
stone in place and of affording room for vehicles to pass each other. 
To improve the shoulders for the second purpose, they are some- 
times covered with a thin coat of gravel to harden the surface. 
Sand shoulders are speedily hardened by the infiltration of fine stone 



192 WATER-BOUND MACADAM ROADS [CHAP. VI 

dust and dirt washed from the surface of the road. This effect is 
quite noticeable with coarse sand; and is appreciable even with fine 
sand. 

354. Crown. The center of the road should be higher than the 
sides, so that the water from rains may flow rapidly into the side 
ditches. If originally too flat, the road is soon worn hollow, and 
the middle becomes a pool if on level ground, or a water course 
if on an inclination. In the former case the middle of the road is 
sloppy; and in the latter, the fine material washes away and leaves 
the larger stones bare. There has been much discussion both as to 
the proper amount of crown and the exact form of the transverse 
profile of the roadway. 

355. Form of the Crown. Some claim that the upper surface 
should be curved, and others that it should be two inclined planes 
meeting at the center of the road and having their angle slightly 
rounded off. Both forms are in common use; the first is the more 
common, but apparently the latter is the better. 

The following objections are urged against the curved profile: 
1, The greater slope near the side causes vehicles to seek the center, 
and consequently the road wears unequally. 2. Owing to the excess 
of travel at the center, the road soon wears hollow and holds water, 
which is both unsightly and a damage to the road. 3. The slope 
is so slight near the center that a small settlement of the subgrade 
causes a depression of the surface, which holds water. 

The only objection to a surface composed of two planes is that 
the flanks wear hollow and hold water; but this objection has less 
force than any of the three against the curved profile. 

Regularity and evenness of crown is more important than the 
mathematical form of the cross section. A sHght depression be- 
comes very conspicuous when filled with water; and besides the 
water standing upon the surface softens it and tends to increase 
the depression. With a little care in filling the low places devel- 
oped during the rolling, it is possible to build a broken-stone road 
with an almost mathematically exact crown. 

356. Amount of Crown. The proper amount of crown depends 
chiefly upon the method of making repairs. If new material is 
added only, say, each second or third time the surface is smoothed 
up, then the crown should be greater to compensate for future 
wear; but if new material is added practically continuously, the 
crown may be considerably smaller. The rate of transverse slope 
should be smaller on wide than on narrow streets, to prevent the 



^RT. 2] CONSTRUCTION 193 

water from unduly washing the surface near the sides. There 
should be more crown on steep grades than on flat ones, to throw 
the water quickly to the side ditch and to prevent it from flowing 
down the grade on the surface of the road and washing out the 
binder. 

Sometimes wide boulevards, with curved profile and maintained 
by continuous repairs, have a crown of one sixtieth of the width, or a 
rise of 0.4 inch per foot from side to center, or an average slope of 
1 in 30. The French roads, which have a curved profile and are 
maintained by the system of continuous repairs, have a crown of one 
fiftieth of their width, or a rise from side to center of 0.5 inch per 
foot or a slope of 1 in 25. Many of the better cared for streets and 
park drives have a crown of one fortieth, or a rise from side to center 
of 0.6 inch per foot or an average slope of 1 in 20. On the state-aid 
roads in Massachusetts (narrow roads and continuous repairs), the 
surface consists of two planes meeting in the center, the transverse 
slope being f inch to a foot or 1 in 16. Broken-stone roads made of 
soft stone and maintained by periodic repairs frequently have an 
original crown of one twelfth — an average slope of 1 inch to 1 foot 
or 1 in 12. 

357. With a broken-stone road, the method of making repairs 
has more weight in determining the amount of the crown than in the 
case of either an earth road or a gravel road. The earth road is easily 
and cheaply maintained by what may be called the system of con- 
tinuous repairs with the road drag, which restores or rather main- 
tains the crown. With a gravel road, when it is necessary to restore 
the crown by adding more gravel, it is usually sufficient to put on 
only a thin la3^er and wait a comparatively short time for travel to 
consolidate it. With a water-bound macadam road, if the crown or 
rather the surface is to be perpetually maintained, it is necessary to 
keep a man upon a short stretch of the road practically all of the 
time, adding thin patches of stone in first one place and then another, 
a method so expensive that it is practiced in this country only on 
park drives, boulevards, etc.; and if the crown is to be restored 
periodically, it is necessary to add a considerable layer of stone and 
consolidate it by long continued and expensive rolling and sprinkling, 
and on account of the expense of this operation and the obstruction 
to traffic it is customary to lay such a thickness of stone and to give 
the surface such a crown as not soon to require a repetition of the 
process. Therefore it happens that broken-stone roads are often 
built with a crown nearly, if not quite, equal to that of good 



194 WATER-BOUND MACADAM ROADS [CHAP. VI 

earth roads, and with more perhaps than is given to good gravel 
roads. 

358. There is a shght advantage of a very high crown for a broken- 
stone road, particularly for one that is not frequently cleaned. If 
the crown is great, the rains will the better wash the surface. Dirt 
upon the surface is not only unsightly, but is also detrimental since 
it holds the water and softens the surface. Of course the material 
washed by rains into the gutter must eventually be removed; but 
this can be removed more cheaply from the gutter at comparatively 
long intervals, than from the surface with brooms or scrapers at 
short intervals. The practice of making a high crown is somewhat 
common in villages using soft road metal and having earth gutters 
and only surface drainage. 

This advantage of a high crown is less for a country road than 
for a village street, since the wind usually gets a better sweep at the 
former than at the latter. 

359. Super-elevation on Curves. For a rule for the super-eleva- 
tion of the road surface on curves, see § 90. 

360. THICKNESS. The object of placing a layer c: broken 
stone upon the trackway is to secure (1) a smooth hard surface, 
(2) a water-tight roof, and (3) a more or less rigid stratum which 
will distribute the concentrated pressure of the wheel over so great 
an area of the subgrade that the soil can support the load without 
indentation. The smoothness and tightness of the surface depends 
upon the quantity and quality of the binding material (§ 383-87), 
and the rigidity of the layer depends somewhat upon the binder, 
but chiefly upon the thickness of the stratum. The supporting 
power of the subgrade depends upon the nature of the soil and the 
drainage. Therefore the minimum thickness of broken stone depends 
upon the nature of the soil, the drainage, the traffic, and the binding 
material; and the initial thickness depends upon the amount of wear 
permitted before new material is added. If repairs are continuous, 
the initial thickness may be the minimum; but if repairs are made 
periodically, the initial thickness must be equal to the minimum 
thickness plus the amount allowed for wear. After a road has been 
worn down 3 inches, it is usually so uneven as to require re-surfacing; 
and therefore it is uneconomical if the road in this stage is much or 
any thicker than the minimum required to prevent its breaking 
through. 

There has been much discussion and there is a great difference 
of opinion as to the proper depth of a broken-stone road. The 



ART. 2] CONSTRUCTION 195 

depth considered necessary by the most extreme advocates of thick 
roads has decreased with the introduction of more improved methods 
of construction — particularly the use of binder and a steam roller, — 
and as the advantage of thorough underdrainage has been better 
appreciated. Early in the last century a depth of 18 to 24 inches 
was frequently considered necessary for heavy traffic, but later it 
was reduced to 12 or 15 inches, while now 6 inches, or less, is usually 
considered sufficient. 

361. Theoretical Thickness. The concentrated load of a wheel is 
transmitted through the broken stone to the earth in lines diverging 
downward, and the wheel may be assumed as resting upon the apex 
of a cone whose base is upon the earth subgrade. It is not wise to 
attempt to find a mathematical relation between tht, load on the 
wheel and the resulting pressure on the earth, since neither the 
angle of the cone nor the distribution of the pressure on the base 
of the cone are known. 

The Massachusetts Highway Conamission assumes the concen- 
trated load to be uniformly distributed over an area equal to the 
square of twice the thickness of the layer of crushed stone, which is 
equivalent to assuming that the sides of the cone make an angle of 
48 1 degrees with the vertical and that the pressure is uniformly dis- 
tributed over the base. According to this theory, if t = the thick- 
ness of the stone in inches, w = the maximum weight in pounds 
per wheel, and p = the supporting power of the soil in pounds 
per square inch, then 

t -S • (1) 

The Commission has applied this formula to roads already con- 
structed to determine the safe bearing power of the soil, and con- 
cludes that non-porous soils, drained of ground water, at their 
worst will support a load of 4 lb. per square inch, and that sand and 
gravel will safety support 20 lb. per square inch.* 

Although the method of arriving at equation (1) is not correct, 
the manner of deducing the supporting power of the soil in a measure 
offsets the error, and consequently the formula may be used with 
some confidence. 

362. Actual Thickness. In Massachusetts the thickness for 
state-aid roads varies from 4 to 16 inches, the standard for crushed 

* Massachusetts Highway Commission, Report for 1901, p. 15. 



196 



WATEK-BOUND MACADAM ROADS 



[chap. VI 



stone with macadam foundation on well-drained sand or gravel being 
6 inches, " which appears to be ample for the heaviest traffic." 

In New Jersey, on state-aid roads, the depth of stone with mac- 
adam foundation varies from 4 to 12 inches, but is generally 6 inches; 
and the telford roads are from 8 to 12 inches thick, usually 8 inches. 
Most of the roads have a macadam foundation, the telford being 
used as a rule only where field stones suitable for a telford foundation 
are found alongside of the road. 

363. The experience at Bridgeport, Conn., has been frequently 
cited to prove that a comparatively thin road is sufficient. Some- 
thing like 60 miles of 4-inch macadam roads built in that place gave 
excellent service even under heavy traffic. The conditions were 
very favorable for a thin road: (1) the soil was sand or sandy loam, 
and had fairly good natural drainage; (2) the subgrade was thor- 
oughly rolled with a 15-ton roller; (3) the broken stone was trap, 
which is hard and durable; (4) the binder was hard and durable, 
being either stone dust or siliceous sand, and was free from clay or 
loam; (5) the binder was worked in until the voids in the crushed 
trap were practically filled, the effect of frost being thus reduced to a 
minimum and the soil being prevented from working up from below; 
(6) the stone was thoroughly consolidated with a steam roller of 
adequate weight; and (7) the roads were maintained by the system 
of continuous repairs. 

The experience at Bridgeport has been repeated at several other 
places; but such experiences should be regarded as the exception, 
rather than the rule, since 4-inch roads are adequate only under 
favorable natural conditions and with the most painstaking con- 
struction and careful maintenance. The fact that a very thin road 
can carry the traffic does not prove that such a road is the most 
economical, for the increased cost of maintenance may more than 
counter-balance the decreased cost of construction. The engineer 
should always attempt to construct economically and adapt his 
construction to fit the natural conditions. 

364. Wings. In the preceding discussion of the thickness of 
the road metal it has been assumed that the depth was practically 
uniform; but some engineers, in recognition of the fact that there is 
less travel nearer the sides than at the center, make the thickness of 
a strip on each side considerably less than that at the center. The 
thin strips on the sides are called wings. Fig. 48, a portion of the 
Swedesboro road in Gloucester County, New Jersey, shows a cross 
section of this form. This construction is somewhat common in 



ART. 2] 



CONSTRUCTION 



197 



New Jersey, both with telford and macadam foundations, and has 
been adopted by the U. S. A. engineers for macadam roads in Porto 
Rico. The wings are usually 2 or 2J feet wide. A road with wings 



>--- 7ft. *{'Z5/?>}< 9ft. >fZ5ft^ — 7 ft H 




i 



Fig. 48. — New Jersey Telford Road with Macadam Wings. 
0.»f.4ff.-yf. ZOff to 26 ft Rolled ^4ft.^'^ft'^ 




I 



Fig. 49. — Standard Section for New York State-aid Roads. 

is simply a compromise between a narrow thick road and a wide 
thin one. 

365. EXAMPLES OF CROSS SECTIONS. Fig. 46, page 191, shows 
a cross section of a telford road built under Telford's direction in 



2ft.^5ft-yf3ft.-^ 4.5ft ->t^ 4.5ft ->^ 4.5ft->\^45tt->f3ft->f5fti*2ft.^. 




Fig. 50. — General Section of Flushing and Jamaica Road. 







Fig. 51. — Standard Section in Excavation for Massachusetts State-aid Roads, 



1815. Fig. 47, page 191, shows a New Jersey telford road. Fig. 
48 shows a telford road with macadam wings. Fig. 49 shows the 
standard cross section for state-aid roads in the State of New York. 
Fig. 50 is a section of a road in Flushing, Long Island, near New York 



198 



WATER-BOUND MACADAM ROADS 



[chap. VI 



City. Fig. 51 and 52, are the standard cross sections in excavation 
and on embankment, respectively, for state-aid roads in Massachu- 



- 25 ft 




LONGITUDINAL SECTION 
Fig. 52. — Standard Section on Embankment for Massachusetts State-aid Roads. 



-tn-iil'in-^isfi-^t^-- laft 




Fig. 53. — Class-II Road, Canton of Bern, Switzerland. 




ten. 



^isfti. 



^^^ ^!mYr\<ik n \i^\\'^^ 



Fig. 54, — Class-III Road, Canton of Bern, Switzerland. 




pfi20M0^—6ff. 7h-^ QfflOir) ^--dfUOn ^ - m'7//? -^i^pii^fi^ 




S/opelfol -^ "^Z^. 
Fig. 55. — Typical Road in Department of Bas-Rhin, France. 



setts. Fig. 53 and 54 show two Swiss roads. Fig. 55 shows a typi- 
cal road in the Department of Bas-Rhin, France. The broken 



ART. 2] CONSTRUCTION 199 

stone is 6 inches deep. Fig. 56 is a typical French road in the 
Department of Seine-et-Oise. 




Fig. 56. — Tpyical Road in Department of Seine-et-Oise, France. 

366. Permissible Grades. For a general discussion of the 
subject of maximum and minimum grades, see § 79-86. The fol- 
lowing examples of maximum grades for water-bound macadam roads 
are instructive. 

In France the standard is: on national roads, not exceeding 
3 per cent; departmental roads, not exceeding 4 per cent; and 
subordinate roads, not exceeding 6 per cent. On the great Alpine 
road over the Simplon Pass, built under the direction of Napoleon 
Bonaparte, the grades average 1 in 22 (4|%) on the Italian side, 
and 1 in 17 (5.9%) on the Swiss side, and in only one case become 
as steep as 1 in 13 (7.7%). 

In Great Britain, the celebrated Holyhead road, built by Tel- 
ford through the very mountainous district of North Wales, has an 
ordinary maximum of 1 in 30 (3|%), with one piece of 1 in 22 (4|%) 
and a very short piece of 1 in 17 (5.9%), on both of which pieces 
special care was taken to make the surface harder and smoother 
than on the remainder of the road. 

On the National Pike over the AUeghenies, built before the intro- 
duction of the railroad, the maximum was 7 per cent. At an early 
day the New York law limited the grades of turnpikes (toll roads) to 
1 in 11 (9%). 

In New York on state-aid roads the nominal maximum is 5 per 
cent, but grades as steep as 6| per cent have been found necessary 
in some cases. In New Jersey are a number of state-aid roads having 
grades of 7 and 8 per cent, and one has lOf per cent. In Massa- 
chusetts no hard-and-fast standard has been adopted for the state- 
aid roads, but a few have 5 per cent grades and a considerable num- 
ber have 4 per cent grades. It is said that on some important 
Massachusetts roads the grade can not at reasonable expense be 
reduced below 7 per cent. 

367. In improving city streets it is often impossible to make any 
radical change in the grade owing to the resulting damage to abut- 



200 



WATEK-BOUND MACADAM ROADS 



[chap. VI 



ting property, and it is almost impossible to avoid the steep grade 
by a change of location; and consequently some city streets have 
very steep grades which are used with surprisingly good results. 
Newton, Mass., has a number of water-bound macadam streets 
which have long stretches of 9 and 10 per cent grades, and has one 
12 per cent grade 1,000 feet long. Waltham, Mass., has one 400- 
foot stretch of water-bound macadam on a 12 per cent grade, and 
another on a 13 per cent grade. In the Borough of Richmond 
(Staten Island), New York City, are several pieces of 10, 11, and 12 
per cent grades, and 100 feet of 14 per cent, two stretches of 200 feet 
each of 16 per cent, and one piece 200 feet long of 20 per cent grade. 

368. Preparing the SUBGRADE. The broken stone is designed 
to take the wear of hoofs and wheels, but the earth foundation must 
support the load; and therefore any road which is constructed with- 
out giving due attention to the earth road-bed is wrong from the 
start, and will never be a good road until the defect is remedied. 

For instructions concerning the construction of embankments 
and excavations, see § 132-35. In building an embankment upon 
which broken stone is to be laid, every reasonable care should be 
taken to prevent uneven settlement. It is sometimes advisable 
to delay the laying of madacam for at least a year in order to give 
the embankment time to settle, for it is impossible to construct an 
embankment of earth more than a few feet in height without having 
subsequent settlement. If this settling took place evenly all along 
the embankment, no particular harm would be done to the mac- 
adam laid upon it; but owing to the difference in the soils composing 
embankments and also in the way the earth is dimiped, there is 
always a tendency for some parts to settle more than others. 

Sometimes the road surface is placed so low that it forms a gutter 
to drain the adjacent fields, which of course is very objectionable. 
Occasionally the earth from the side ditches and from the trench in 
which the stone is placed, is deposited at the side of the right-of-way 
instead of being used to raise the road surface. In this connection, 
see § 139. 

369. After the subgrade has been brought to the proper form 
(§ 351), it should be rolled thoroughly — both to consolidate it and to 
discover soft spots. For a discussion of road rollers, see § 378-79. 

Fig. 57 shows the method of smoothing the subgrade with a 
scraping grader; and also shows the rolling of the shoulder. Fig. 
58 shows the subgrade after the rolling is completed. 

In rolling; quicksand spots are sometimes discovered, in which 



ART. 2] 



CONSTRUCTION 



201 



case the troublesome material should be excavated and suitable 
material substituted. If the road-bed be of sand or of material of 
such a nature as to push along in a wave in front of the roller, a 
thin layer of broken stone or gravel strewn over the surface will 




Fig. 57. — Smoothing Subgrade and Rolling Shoulder. 




Fig. 58. — Subgrade Rolled and Ready for Stone. 



enable the roller to consolidate the road-bed. If the surface is clay 
that sticks to the roller, sprinkle a thin layer of sand or cinders 
over the surface. If the clay is soft and forms a wave in front of the 
roller, additional rolling is a detriment, as it increases the plasticity 
of the clay. 

370. Setting the Telford. The distinguishing feature of a 
telford road is its paved foundation. After the road-bed has been 
brought to the proper form and been rolled, rough stones are set 
upon the surface to form a pavement 5 to 8 inches thick, the thick- 
ness depending upon that to be given to the finished road (§ 360), 
the general practice being to make the paved foundation about two 
thirds of the total thickness of the road. The practice of Telford 



202 WATER-BOUND MACADAM ROADS [CHAP. VI 

was to grade the road-bed flat, and then construct his pavement 
deeper in the middle than at the sides, using for a roadway 16 feet 
wide, stones about 8 inches deep at the middle and 5 inches at the 
sides. This practice is still followed by some engineers; but it is now 
more common and usually considered preferable to make the surface 
of the road-bed parallel to the finished surface, and the pavement of 
uniform thickness. Fig. 46, page 191, shows a telford road with a 
level subgrade; and Fig. 47, page 191, a telford road with the sub- 
grade parallel to the finished surface. 

The size of the stones for the telford pavement is of no great 
importance, at least there is a great difference in the practice of the 
best road builders. The width of the stones varies from 3 to 10 
inches, 3 to 6 being most common; and the length varies from 6 
to 20 inches, 8 to 12 being most common. It is desirable to have 
the width on any particular job somewhat nearly uniform, and the 
stones in any course should be still more nearly equal. The stones 
are set upon their widest edge with their greatest length across the 
road, the joints being broken as much as possible. Each stone 
should stand independently of its neighbor, i. e., one stone should 
not lean against another. The irregularities of the upper surface 
are then broken off with a hammer, and the interstices between 
the stones are filled with spalls lightly driven into place with a ham- 
mer or a crow-bar. This knocking off of the projecting points and 
the driving of spalls into the interstices should not be done so near 
the face of the pavement as to dislocate the stones last set. It is 
frequently specified that no wedging shall be done within 10 or 15 
feet of the front edge of the pavement. After the projecting points 
have been knocked off and the interstices have been filled with stone 
chips or ordinary crushed stone, the pavement is usually rolled. It 
is usually specified that the roller shall not go nearer to the front of 
the pavement than 25 to 30 feet. 

The cardinal requisite of a telford foundation is the interlocking 
of the stone closely and compactly together by barring, wedging, 
and rolling until the entire structure is brought in action to resist 
disturbance as a single mass. 

371. Crushing the Stone. The introduction of a machine 
for breaking the material greatly cheapened the cost of broken- 
stone roads. The rock crusher was introduced into America in 
1860, before which time the stone was broken by hand with ham- 
mers on the side of the road. Coincident with the introduction 
of power for breaking the stone, came the revolving screen which 



ART. 21 



CONSTRUCTION 



203 



permitted the fragments to be assorted as to size — an important 
feature, as will soon be shown. 

372. Forms of Crushers. There are two types of crushers now 
in common use. The older one, often called the Blake after the 
original inventor, consists of a strong iron frame, near one end of 
which is a movable jaw. By means of a toggle-joint and an eccen- 
tric, this jaw is moved backward and forward a slight distance. As 
the jaw recedes the opening increases and the stone descends; as the 
jaw again approaches the frame, the stone is crushed. The maxi- 
mum size of the product is determined by the distance the jaw plates 




Fig. 59. — Oscillatory Stone Crusher. 



are from each other at their lower edge. This machine is also fre- 
quently called the oscillatory breaker, or jaw breaker. Fig. 59 shows 
one form of this type. The size of the product is regulated by 
raising or lowering the wedge 10, or by inserting a different pair of 
toggles, — 7. 

The second form of crusher, called the Gates after the original 
inventor, consists of a solid conical iron shaft which is supported 
within a heavy iron receptacle shaped somewhat like an inverted 
bell. By means of an eccentric bearing a rocking and rotary motion 
is given to the shaft, so that each point of its surface is successively 
brought near to and removed from the surface of the bell, which 
causes the stone to be successively crushed as it descends. Fig. 60 



204 



WATER-BOUND MACADAM ROADS 



[chap. VI 



shows one form of this type of crusher. An adjustment permits a 
variation in the size of the product. This form is often called the 
rotary breaker or gyratory breaker. 

It is not wise here to consider the relative merits of the different 
forms and sizes of stone crushers, the power required, the output. 



.-'^s 




":l^--lj 



Fig. 60. — Gyratory Rock Crusher. 



etc., since the construction of a reasonably good macadam road 
requires a large equipment of machinery and an experienced con- 
tractor, and since the equipment varies with the conditions. 

Fig. 61 gives a hint as to the arrangement of the crusher, the 
elevator, the screens, and the storage bins. Fig. 62, shows a real 
crushing plant at Green Lake, Wis. 

373. Sizes of Stone. The size of stone used for road metal 
depends upon the hardness and toughness of the stone and upon 
the weight of the traffic. The harder and tougher the material, 
the smaller it may be broken without danger of its crushing or shat- 



ART. 2] 



CONSTRUCTION 



205 




Fig. 61. — Diagrammatic Arrangement of Stone-crushing Plant. 




Fig. 62. — Stone-crushing Plant. 



206 



WATER-BOUND MACADAM ROADS 



[chap. Vf 



tering under the load of wheels and the impact of hoofs; and the 
harder and tougher a stone, the smaller it must be broken in order 
that it may compact well in the road. The stones in the top course 
should be larger for heavy traffic than for light traffic, to prevent 
their being ground to powder. Larger stones c?,n be used in the 
bottom layers of a road than at the top. 

One of MacAdam's rules was to exclude any fragment weigh- 
ing more than 6 ounces. A 1 J-inch cube of compact limestone weighs 
about 6 ounces. Another of MacAdam's rules was to exclude any 
stone that could not readily be put into a man's mouth. These rules 
are frequently quoted, even now, although improvements in road 
machinery have made them inappropriate with present methods. 

The bottom course of a macadam road built of soft stones is 
often composed of fragments 3 to 4 inches in greatest dimensions; 
but if it is built of hard tough stone, the sizes are 2 to 2| inches. 
The size of rock in the lower courses is not so important as that for 
the surface course (see § 374). The top course of hard tough stones 
is usually 1 to 2 inches for heavy traffic, and J to 1 inch for light 
traffic. 

The custom is to lay the stone in courses of substantially one size, 
although some road builders prefer to have the sizes mixed when 
thrown into the road. The only advantage of the latter practice is 
that with a skilful proportioning of the sizes less rolling is required; 
but it is objectionable owing to the difficulty of getting the several 
sizes properly proportioned and keeping them thoroughly mixed. 
There is generally too much fine material in the mixed sizes, which 
makes the road wear rapidly and imevenly. 

Connected with the crusher and run with the same power is 
generally a rotary screen having meshes of three sizes — usually 
about J, IJ, and 2^ inches. 

374. For economic reasons the size of stone in the several courses 
and their thickness should be adjusted so as to use, if possible, all 
of the output of the crusher. The output of the various sizes varies 
considerably with the character of the stone. With a hard stone, 
half or more of the product of the crusher will not pass through the 
|-inch screen; while with field stones one half may pass through 
such a screen. The last gives more '' fines " or '^ screenings " 
than can be used profitably during construction, but the surplus is 
very useful in maintaining the surface. With some rocks it is diffi- 
cult to get enough fine material for use in the original construc- 
tion. 



ART. 2] 



CONSTRUCTION 



207 



375. Spreading the Stone. The stone is usually hauled 
from the crusher to the road m wagons or trucks, dumped upon the 
roadway, and spread with forks or rakes. Dumping in place is objec- 
tionable, since the coarse and fine fragments become separated in 




Fig. 63. — Auto Truck Dumping Stone. 



the process, producing a layer of unequal density and an irregular 
surface after rolling. It is sometimes specified that the stone 





Fig. 64. — Spreading Stone with Rakes. Fig. 65. — Spreading Stone with Shovels. 



shall be dumped upon a platform, from which it is distributed 
with shovels. This method of spreading costs 4 to 6 cents per 
cubic yard — about twice that by dumping and raking and is 
appropriate only when the very best results are sought. Wagons and 



208 



WATER-BOUND MACADAM ROADS 



CHAP. VI 



trucks are upon the market which can automatically dump and dis- 
tribute the stone in layers of uniform thickness; but owing to their 




Fig. 66. — Shuart Grader. 



cost and weight they are not in very general use. Fig. 63 shows an 
auto truck dumping the stone in a ridge on the subgrade. 

The stone is sometimes spread by hand with rakes and shovels — 
see Fig. 64 and 65. Notice the template in Fig. 65 used to gage 
the thickness of the layer of stone. 

There are several methods of spreading the stone by machinery. 
Some contractors use the Shuart grader, Fig. 66, a machine that 





Fig. 67. — Harrowing Stone.' 



FIG 



i8. — Leveling Stone with 
Scraping Grader. 



was devised for use in leveling ground that is to be irrigated. 
Other contractors level the stone with a harrow as shown in Fig. 67. 



ART. 2] 



CONSTRUCTION 



209 



Still other contractors use a scraping grader to level the stone — 
Fig. 68. Fig. 69 shows the bottom course of stone ready for rolling. 
The stone should be applied in uniform layers, the thickness 
of each depending upon the total thickness of the road. Two 
methods are in use for gaging the thickness of the layers of stone. 
1. On the finished subgrade, wood cubes of a depth equal to the 
thickness of the layer are set at frequent intervals, and the loose 




Fig. 



. — Bottom Course Ready foe Rolling. 



stone is laid even with the tops of these blocks. This method is 
sometimes described as building by blocks, and is the one employed 
on the state-aid roads of New Jersey. 2. The soil is brought to an 
established grade, and the finished road is required to be brought 
to another established grade, in which case neither the absolute 
thickness nor the uniformity of the several courses is a matter of 
much importance. This method is employed on the state-aid roads 
in Massachusetts. 

376. SHRINKAGE IN ROLLING. Before beginning to spread the 
layers of stone, it is necessary to determine the amount the crushed 
stone will shrink in rolling. The shrinkage has an important bearing 
upon the thickness and cost of the finished road; but great errors 
are sometimes made in estimating the amount of shrinkage. The 
following examples from practice show the actual shrinkage. 



210 WATER-BOUND MACADAM ROADS [CHAP. VI 

In one case,* with trap rock 1| to 2J inches, rolled with a 12|-ton 
steam roller upon a subgrade so hard that the wagons hauling the 
stone made no ruts, 5.67 inches of loose stone rolled to 4 inches, 
and 7.38 inches rolled to 6 inches. The average thickness of the 
loose stone was determined by dividing the quantity of stone used 
by the area covered. The first is a shrinkage of 29 per cent and 
the second of 19 per cent. The difference between these two results 
is probably due to errors of observation, to variations in the thick- 
ness of the finished road, and to the fact that the thicker layers did 
not compact as solidly as the thinner ones. The stone was rolled 
dry until the desired thickness was reached, when the binder was 
added, and sprinkling was commenced. 

In another case,t with 2-inch trap laid on the compact siu"face 
of an old crushed-stone road and rolled with a 12-ton roller, 3.9 
inches of loose stone roUed to 3 inches. The shrinkage was 23 per 
cent. The thickness was determined from the area covered and 
the quantity of stone used. No stone could have been forced into 
the subgrade, but there was some uncertainty as to the average 
elevation of the surface of the old street. 

It has been determined J by tests over several miles of road 
where the output of the crusher was carefully measured in wagons 
and also when rolled in place, that 6 inches of loose hard Umestone 
rolled down to 4| inches, which is a shrinkage of 20 per cent. 

377. It is probable that the maximimi actual shrinkage in rolling 
is less than 20 per cent. The apparent shrinkage depends upon the 
nature and condition of the subgrade, i. e., upon the amount of stone 
forced into the earth. 

If the soil is clay, the sprinkling required to work the binder 
into the interstices may soften the subgrade so that considerable 
stone will be forced into the earth. This condition is indicated by 
the roller's leaving tracks upon the surface; and when this occurs, the 
work should be stopped until the subgrade dries out. To prevent 
the crushed stone from being forced into the clay subgrade during 
construction or after completion — particularly when the frost is 
going out, — a layer of sand, stone screenings, ashes, or the like, 
is sometimes interposed. The English engineers often use " hard 
core " (a mixture of brick rubbish, old plastering, and broken stone) 
on a clay soil, to prevent the mud's working into the metaling. Any 

* W. C. Foster in Trans. Amer. Soc. of Civil Eng'rs, Vol. 41, p. 135-38. 

t F. G. Cudworth in Trans. Amer. Soc. of Civil Eng'rs, Vol. 41, p. 126-28. 

t H. P. Gillette in Economics of Road Construction, p. 19-20. New York, 1901. 



ART. 2] CONSTRUCTION 211 

material not affected by water is useful for this purpose; and the 
finer it is the better, since the smaller will be the apertures in it, and 
the more certainly will it prevent the soil from coming up through it. 

If the soil is sandy, a thin layer of coarse gravel or broken stone 
laid upon the surface and then rolled, will prevent any further loss 
of the road metal in the subgrade. If the soil is nearly pure sand, 
the wetter it is the less crushed stone will be forced into it; and 
therefore if water is plentiful, it may be wise to keep the sand satu- 
rated while the rolling is in progress to prevent the loss of the stone. 
The Massachusetts Highway Commission used cotton cheese-cloth 
on a soft fine sand to prevent the stone from sinking into the sub- 
grade. '^ It is not at all needful that the partition should be endur- 
ing, for as soon as the stones in the lower layer have been forced 
into contact and have become bound together, there is no further 
danger of the mingling of the stone with the sand; and hence the 
decay of the fabric is a matter of no consequence. The cloth was 
spread in strips lengthwise of the way; and the stone for the bottom 
layer was shoveled from the sides upon it with no unusual care. A 
section through such a road showed that the stones did not tear 
through the cloth. At 3 cents per square yard on the road, the cost 
of the cloth may be less than one third that due to the loss of the 
broken stone which would occur if it were allowed to come directly in 
contact with the sand. Various kinds of strong paper were tried, 
but found worthless." A thick coating of straw has been used to 
hold up the macadam on a sandy soil. 

However, if the sand is firm enough to hold up the stone during 
the rolling, it is not necessary to prevent the mixing of the sand 
and the stone, since the subgrade may be left a little high, with 
the expectation of forcing the stone into the sand. This is equiva- 
lent to using the sand of the subgrade as a filler or binder for the 
lower portion of the broken stone. If the sand is dry and nearly 
pure, it can be thus forced nearly to the top of a 4-inch course of 
coarse broken stone. 

378. ROAD Rollers. The roller is indispensable for the eco- 
nomic construction of water-bound macadam roads. Roads can be 
built without the use of a roller, but alwaj^s at large expense to the 
traffic and with great waste of the road metal; and such roads never 
have as smooth a surface and are not as durable as if a roller had been 
employed in their construction. With traffic-consolidated roads, 
much of the metal is worn round and smooth before the fragments 
become firmly fixed in place ; and the dirt brought upon the road by 



212 



WATER-BOUND MACADAM ROADS 



[chap. VI 



the traffic mixes with the stone and prevents it from ever packing as 
sohdly as the clean stone would, and, besides, the dirt when wet 
has a lubricating effect upon the stone which under the action of 
traffic causes the surface to break up readily. Further, during 
the time travel is consolidating the stone, the surface is not even 
approximately water-tight; and therefore the subgrade is softened by 
rains, and the stone is mixed with the earth below and virtually lost. 




Fig. 70. — Three-Wheel or Macadam Roller, 



Ordinarily, it is true economy to compact the road by the use of a 
roller. 

Formerly both horse and steam rollers were employed; but now 
only the latter are used. There are two type forms of steam, or 
rather power, road-rollers — see Fig. 70 and 71. The first, or three- 
wheel type, is the form employed in macadam road construction; 
and the second, or tandem type, is the form used in rolling asphalt 
pavements and other bituminous road surfaces. Both types are 
driven by steam or by gasoline, but the latter is rapidly gaining in 
favor. There are a variety of forms of each type, but the essential 
features of all are practically the same. 

The total weight of the macadam roller varies from 7 to 15 tons; 
and the pressure under the drivers varies from 300 to 500 lb. per linear 
inch. The total weight of the tandem roller varies from 2J to 10 



ART. 21 



CONSTRUCTION 



213 



tons, and the pressure under the driving drum from 125 to 300 lb. 
per Hnear inch and for the hghtest roller the compression under the 
steering drum is usually about 60 lb. per linear inch. Of the tandem 




^ ■'^vK'^y 'i.^was 



Fig. 71. — Tandem or Asphalt Roller. 



type the 5- and 8-ton roller are most common, and give a pressure 
under the driving drum of about 200 and 280 lb. per inch respectively. 

379. The weight of the roller should be proportional to the hard- 
ness of the stone, as too heavy a roller crushes the material instead of 
compacting it. An excessively heavy roller will sometimes sink into 
light or loose soil, and force it ahead in a wave which the roller can not 
surmount. This may sometimes be prevented by spreading a thin 
layer of sand or gravel on the surface being rolled. A similar dif- 
ficulty sometimes occurs with a heavy roller on a layer of loose 
stones. If the front wheels or rollers of the machine were larger, 
this difficulty would be decreased. In localities where the soil is of a 
loose sandy nature, a roller weighing 10 or 12 tons is usually preferred; 
and in districts where the soil is stiff or gravelly clay, a weight of 12 
or 15 tons is used. In localities where the road material is hard, a 
15-ton roller is necessary; but with the softer stones a weight of 10 
or 12 tons is sufficient. 

380. ROLLING THE STONE. Rolling is a very important part of 
the construction of a water-bound macadam road. The subgrade 
should be rolled to prevent the stones' being forced into the earth. 
The lower course of the stone should be rolled to compact it so that 
the pieces will not move one upon the other under the traffic and the 
top course should be rolled to pack or bind the pieces into place. 



214 



WATER-BOUND MACADAM ROADS 



[chap. VI 



Rolling accompanied by sprinkling (see Fig. 72) is necessary also 
to work the binding material into the interstices so as to make the 
surface water-tight. Roads that have been consolidated by traffic 
are largely held together by mud, and after long use are fairly 
smooth and hard in dry weather, but become soft and muddy dur- 
ing a wet time. 

The stone is put on in two or three layers, — according to the total 
thickness of the finished road, — and each course is thoroughly rolled 




Fig. 72. — Sprinkling and RoLuraJG. 



before the next is added. No course should be more than 4 to 6 
inches thick. When a telford foundation is used, broken stone is 
spread over the pavement to bring the top surface to the proper 
form and height, after which it is rolled. 

381. The rolling should proceed gradually from both sides toward 
the center. If the weight of the roller can be varied, commence 
with the unballasted roller, and increase the weight as the stone 
becomes consoHdated. If the surface of the layer shows a wavy 
motion after being rolled three or four times, the subgrade is too wet ; 
and time should be given it to dry out. Some coarse brittle granitic 
rocks begin to crawl and the sharp edges to break off after the roller 
has passed over them a few times; but a light sprinkling of sand or 
stone screenings will prevent this, and facilitate the consolidation 
of the layer. All irregularities of the surface developed by the 
rolling should be corrected by filling the depressions with stone of the 
size used in the layer. 

The rolling should be continued until the stone ceases to creep 
in front of the roller, and until the macadam is firm under the foot 
as om walks over it. When the rolling is complete, one of the 



ART. 2] CONSTRUCTION 215 

larger stones of the course can be crushed under the roller without 
indenting the surface of the layer. 

When the first course has been consolidated, a second, usually 
a thinner one of smaller stones, is added ; and then it is rolled the same 
as the first. Finally a third course consisting of about half an inch 
of sand or fine stone and stone dust is added. The roller is then 
passed over this layer, with the result that the bits are ground to 
powder. As the rolling of this course proceeds it is sprinkled, the 
aim of the sprinkling and rolling being to work the fine material 
into the cavities between the pieces of crushed stone, thus binding 
the whole into a solid mass. The proper binding of the road is the 
most important part of the construction, and will be more fully 
considered presently (see § 383). 

382. Amount of Rolling. The total amount of rolling required 
varies with the weight of the roller, the hardness and the size of the 
stone, and the amount of binder and water used. Trap rock being 
very hard requires two or three times as much rolling as most other 
stone. An excess of binding material and of water gives a compact 
surface with comparatively little rolling, but the road is not as dur- 
able as though it had been more thoroughly rolled. 

The following examples are representative of the best American 
practice. 

In New York City, 5 inches of crushed gneiss on telford and 
5 inches of trap on the gneiss, bound with trap screenings, was rolled 
with a 15-ton steam roller at the rate of 40.6 square yards per hour, 
or 10 cubic yards per hour. Although it is common to give the 
amount of rolling in terms of the time required, the statement is 
somewhat indefinite, since the work accomplished varies with the 
speed of the roller and also with the length of run, i. e., with the time 
lost in starting and stopping. The usual speed of steam rollers is 2 to 
2| miles per hour. The above work is equivalent to 0.553 ton- 
miles per square yard, or 2.246 ton-miles per cubic yard. The num- 
ber of trips was 130.* 

In making repairs, a 6-inch course of 2-inch trap was rolled at 
the rate of 26.2 square yards per hour, or 4.4 cubic yards per hour. 
The work amounted to about 0.859 ton-miles per square yard, or 
5.177 ton-miles per cubic yard. The number of trips over the sur- 
face was 201. t 

An area of 22,000 square yards oi a 3-inch course of 2-inch trap 

*Trans. Amer Soc. of Civil Engineers, Vol. 8, p. 105-6. 
f Ibid., p. 107. 



216 WATER-BOUND MACADAM ROADS [cHAP. VI 

upon an old broken-stone road, bound with trap-rock screenings 
and rolled with a 10-ton steam roller, was finished at an average 
rate of 47.15 square yards per hour of rolling, the extremes being 38.4 
and 61.1 square yards per hour. This was an average of about 4.0 
cubic yards per hour. * 

A 6-inch course of 1|- to 2|-inch trap rock, bound with lime- 
stone screenings, was rolled with a 12i-ton steam roller at an average 
rate of 31.4 square yards per hour, or 5.2 cubic yards per hour.f 

The Hudson County Boulevard (Jersey City, N. J.) consists 
of 8 inches of telford, 2^ inches of 2J-inch stone, IJ inches of IJ- 
inch stone, and then J to 1 inch of coarse screenings — all trap rock. 
The macadam top was supposed to roll down to 4 inches, i. e., 4 J 
to 5 inches of loose stone was supposed to roll to 4 inches. The 
rolling was distributed about as follows: On the telford, 10 to 12 
passages; on the 2j-inch course, 8 to 10 passages; on the IJ-inch 
course, 10 to 12; and on the screenings, 80 to 90, — making a total 
of 100 to 120 passages of the roller over the road. 

383. Binding the Road. The interstices between the frag- 
ments of stone should be filled with a fine material which will act 
mechanically to keep out the rain water and thereby keep the 
subgrade dry, and also to support the fragments and prevent them 
from being broken, and which wiU bind or cement the fragments 
into a single more or less sohd mass. The proper binding of the 
stone is the most important part of the construction of a water- 
bound macadam road. 

384. Nature of the Binder. The binding material or the filler 
should be finely divided so as to be easily worked into the interstices, 
should have, a considerable resistance to crushing so as to properly 
support the pieces of crushed stone, and should not change its phys- 
ical condition when wet. Various materials have been employed 
— clay, loam, shale, sand, and limestone and trap-rock screenings. 

Clay and loam are frequently used. Their merit is that they are 
cheap, are easily appKed and have a high cementing power; but they 
are easily affected by water and frost, and when wet act more as a 
lubricant than as a binder. Clay or loam binder will give a smooth 
road without much rolling, but such a road is liable to be very dusty 
in dry weather, and muddy in wet weather. When clay or loam is 
employed as a binder, the utmost care should be taken that no more 
is used than just enough to fill the voids. 

* Trans. Amer. Soc. of Civil Engineers, Vol. 41, p. 127. 
t/6id., p. 138. 



ART. 2] CONSTRUCTION 217 

Shale and slate are only hard and compact clay, and their only 
merit is that they give a smooth surface with but little rolling. They 
are speedily reduced to dust, and then have all the disadvantages 
of clay. They have only fair cementing power. 

Sand is often used as a filler, and if composed of fine, clean, hard 
grains, gives fair results; but sand which is resistant enough for a 
good binding material usually consists of silica or quartz, neither 
of which has a high cementing power. If the grains are coated more 
or less with iron oxide, or if accompanied by bits of ironstone (clay 
cemented with iron oxide), sand makes an excellent binding material, 
since the iron possesses considerable cementing power. This form of 
binder is particularly valuable in making repairs over an opening 
when a roller is not available, or when water for washing in the binder 
is scarce. Low-grade iron ore has been used for a binder — either 
alone or mixed with stone dust. 

Fine screenings — the finest product of the stone crusher, say, 
from J or J inch to dust — from the stone used in the body of the 
course is the most desirable material for a binder, partly because it 
helps to utilize the entire product of the crusher, partly because of 
its high crushing strength, and partly because the stone is usually 
selected for the high cementing power of its dust. Limestone has 
very high cementing power, but is soft and pliable. Trap has a 
fair cementing power, and is hard and durable. Limestone screenings 
require less roUing, but the trap dust makes a more durable road. 

Sometimes the detritus removed from the surface of a stone road 
during maintenance or preparatory to making repairs, is employed 
as a binder. At best, such material is very poor for this purpose. 
It is worn out and has performed its duty; and, besides, it is composed 
largely of manure and vegetable and earthy matter — all of which are 
very undesirable in a binder. Such detritus is more valuable as a 
fertilizer than as a road material. 

385. Applying the Binder. There is a difference of opinion 
among competent engineers as to the best method of applying the 
binding material. Some apply it on the top of each course, and 
some on top of only the last course. In the first case, all the voids 
from the bottom to the top of the road are filled with fine material; 
in the second case, the binder usually fills the voids of the top course 
only. Those who advocate the first method claim that the whole 
mass should be filled to prevent the stones from moving under the 
traffic, and also to prevent the soil from working up from below; 
while the advocates of the second method claim (1) that filHng the 



218 WATER-BOUND MACADAM ROADS [CHAP. VI 

top layer is sufficient to hold the stone in place near the surface, (2) 
that the stones of the lower courses have no tendency to move, (3) 
that the unfilled voids of the lower course promote drainage, and (4) 
that as the upper layer wears away, the dust will wash down into the 
lower open spaces in such a manner as always to keep the 3 or 4 
inches just below the surface properly bound. If the stone is hard, 
or if the lower courses are not thoroughly rolled, applying the binding 
material only on the top of the last course practically fills the voids 
to the earth f oimdation ; but of course it is cheaper to apply the filler 
on the top of each course than to attempt to fill all of the voids by 
applying it on the top course only. If the stone in the lower courses 
is soft, or if the top of the next to the last course is thoroughly rolled, 
applying the binder on the top fills the voids in the top course only. 
It is sufficient to fill the voids of the top course. 

The binder is applied by spreading a layer of " fines " about half 
an inch thick over the partially rolled surface. The filler should 
be dumped upon a board platform, and not directly upon the road 
surface; and should be distributed evenly over the stone with a 
shovel. Under no consideration should loam or vegetable matter 
be allowed to contaminate the stone screenings. After the binding 
material has been evenly distributed, the surface is then sprinkled 
and rolled. The sprinkler should have many fine openings, the 
object being to give a gentle shower rather than a violent flooding. 
The water washes the fine material into the cavities below, and the 
roller crushes the small fragments and makes more dust. The 
rolling also aids in working the binder into the mass; in fact, the 
binder can be worked in to a considerable extent by dry rolling, 
and consequently the quantity of water used varies widely with 
the method of doing the work, but is usually about 4 to 6 cubic 
feet per cubic yard of stone. Sometimes men with heavy brooms 
are kept upon the road sweeping the binding material about to assist 
in working it in, and also to secure a more uniform distribution of it. 
While applying the screenings care should be taken to pick off any 
coarse stone — particularly flat ones, — as they do not bind well and 
their subsequent loosening causes the road to ravel (§ 397). 

As the rolling and sprinkHng proceed, fine material should be 
added where needed, i. e., as open spaces appear. All the filler 
should not be put on in the beginning, since a thin layer can be 
worked in to better advantage than a thick one; and, besides, it is 
desirable to use only enough to fill the voids. 

Occasionally the surface of the road becomes muddy and sticks 



ART. 2] CONSTRUCTION 219 

to the roller. This can be remedied in either of two ways: viz., 
by sprinkling the roller and keeping it constantly wet, or by keeping 
the sprinkling wagon immediately in front of the roller and having 
the binder always fully saturated. The rolling is continued until 
the water is forced as a wave in front of the roller and until the sur- 
face behind the roller is mottled or puddled and is covered with a 
thin paste. The binding, or the puddling of the surface, can not be 
done satisfactorily when the surface freezes nightly. 

When finished, if the road is allowed to dry and is then swept 
clean, the surface will be seen to have the appearance of a rude 
mosaic, the flat faces of the fragments of stone being crowded against 
one another and the interspaces being filled with the binding material 
— the latter occupying about half of the area. Such a surface when 
dry will stand considerable sweeping with a steel broom or brush 
without the fragments of stone being loosened. The water used in 
construction not only aids in working the binder into the interstices, 
but also develops the cementing power of the rock dust. 

386. Usually after the rolling has been completed a thin coating 
of binding material is sprinkled over the surface. Authorities 
differ as to the amount of fine material to be left on the finished 
surface, some specifying as little as | inch and some as much as 
1 inch, the usual quantity being f to J inch. If only enough binding 
material to fill the interstices between the coarser fragments is left 
upon the road, the fine material will be blown and washed away, 
and soon there will not be enough to level up between the large 
bits and to hold the surface stones in place, when the wear will 
come directly upon the stones. On the other hand, if any con- 
siderable quantity of fine material is left upon the surface, it is 
speedily ground up, and becomes offensive dust if it is not sprinkled, 
and equally objectionable mud if it is sprinkled. It is probably 
best to put on a quantity just sufficient to give a thin layer, say, 
i to I inch, over the surface, and when this amount is blown or 
washed away renew it. By this method, the wear on the body of 
the road will be prevented, a minimum amount of sprinkling will 
be required, and there will be as little dust as possible. The surface 
coat is also serviceable in decreasing the tendency of the binding 
material to dry out and to lose part at least of its cementing power. 
Fine material over and above that required to fill the interstices is 
useful only to prevent raveling and to keep the wear from the sur- 
face of the stone ; and therefore sand is as good for the top dressing 
as stone dust, and is usually much cheaper. It is desirable that this 



220 WATER-BOUND MACADAM ROADS [CHAP. VI 

coat of fine material shall be sprinkled and rolled before the traffic 
is admitted. 

The road is now finished; and after it has dried out for a day or 
two, it may be thrown open to traffic. 

387. Amount of Binder. The amount of binder required depends 
upon the hardness of the stone and the amount of rolling preceding 
the application of the binder (§ 385). The voids in the broken stone 
can be reduced by rolling to 20 or 25 per cent, say 22 per cent, of 
the compacted mass; and the completed road will contain 4 to 7 per 
cent, say 5 per cent, of voids; and therefore enough binder must be 
added to fill about 17 (=22 — 5) per cent of voids. The binder 
itself usually contains 40 to 50 per cent of voids, and therefore the 
volume of filler required is 40 to 50 per cent more than the voids to be 
filled, i. e., 40 to 50 per cent more than 17 per cent of the original 
volume of stone; or, in other words, the amount of filler required is 
25 to 35 per cent of the thickness filled. This allows a little for 
waste and for the thin coating spread upon the finished surface. If 
the binder is appHed before the rolling has progressed very far, more 
fine material will be required, since some of it will work in between 
the fragments of stone and prevent them from coming into as close 
contact as they otherwise would. In this case, part of the surplus 
binder will be flushed to the surface during the sprinkling and rolling, 
as mortar flushes to the surface in tamping concrete; but in no case 
does all the surplus thus work out, and consequently the road is not 
as durable as though only enough binder had been used to fill the 
voids; and, further, the binder which flushes to the surface must be 
removed as mud. An excess of binder is often used to reduce the 
cost of construction by decreasing the amount of sprinkling and roll- 
ing required; but such a practice adds to the cost of maintenance, 
and the road is less durable and more dirty. 

388. Cost of Construction. The cost of construction of a 
crushed-stone road varies greatly with the size of the job, the con- 
ditions of the material and labor markets, the specifications under 
which the work is done, etc. It is unwise to give here any details 
as to the cost of the several parts of the work; and only a few data 
will be given concerning the total cost of a road. The total cost 
varies with the amount of grading and drainage required, the length 
improved in a single season, the length of railroad and wagon haul, 
the specifications, the labor market, etc. The following are a few 
representative examples of first-class construction. 

The values here given are somewhat out of date; but present 



ART. 2] CONSTRUCTION 221 

values are quite abnormal owing to the Great European War. The 
data given below are interesting chiefly as showing relative cost in 
different localities and of the different parts of the work. For cur- 
rent prices consult the construction news in technical journals. 

389. New Jersey. In northern New Jersey, the total cost of 
trap macadam roads 4 to 6 inches deep, where the rock was obtained 
near the road, ranged from 20 to 45 cents per square yard; and 
tefford roads consisting of 8 inches of telford and two courses of 
broken stone 2i and IJ inches thick respectively, cost from $1.02 
to $1.29 per square yard. In the southern part of that state, where 
the stone is transported 20 to 70 miles, 8-inch trap macadam roads 
cost from 23 to 70 cents per square yard, the average being from 50 to 
60 cents per square yard.* 

390. Massachusetts. The average cost of 220 miles of state- 
aid roads in Massachusetts built from 1894 to 1899, f reduced to the 

TABLE 27 
Cost of Massachusetts State-aid Water-bound Macadam Roads 

Per Cent 
Items of Expense. . of Total 

• Cost. 

Earthwork at 32.1 cents per cubic yard 16.4 

Rock excavation at $1.80 per cubic yard 2.0 

Shaping earth subgrade at 2.0 cents per cubic yard 2.4 

Gravel for foundation and wings at 55.8 cents per cubic yard 3.5 

Telford foundation at 33.9 cents per square yard 0.2 

_. - ^ ^ ( $1,503 per ton for local stone ) 

Broken stone at •< ^^ „^^ , ,. , V 45. 3 

( $1,920 per ton for trap j 

Side drains at 34.5 cents per lineal foot 2.7 

Rubble masonry — dry, at $3,133 per cubic yard 2.6 

" " in cement, at $5 .770 per cubic yard 3.3 

Guard rails at 16 cents per lineal foot 1.7 

Stone boundary-posts at $1,417 each 0.6 

Paved cobble gutters 66.0 cents per square yard : 1.1 

Vitrified-clay pipe-culverts — 12-inch, at 65 cents per lineal foot 1.2 

Land damages, catch basins, and minor items of construction 3.0 

Engineering and inspection 14 . 

Total 100.0 

equivalent cost of a " standard mile " (15 feet wide), was $9,931.23 
per mile for construction and engineering expenses, exclusive of cost 
of administration and the salaries of the chief engineer and two 

* Compiled from the Reports of the State Commission of Highways of New Jersey, 1895- 
1900. 

t Report of Massachusetts Highway Commission, 1900, p. 150-57. 



222 



WATER-BOUND MACADAM ROADS 



[chap. VI 



assistants. The maximum average for the roads in any township 
was $20,257.48 and the minimum $4,871.30 per ''standard mile." 
The above gives an average cost of $1,126 per square yard, a maximum 
of $2,302, and a minimum of $0,564. 

In Massachusetts in 1897, 52 miles were built in 187 towns 
(townships), the average cost of the several items being as shown 
in Table 27.* An examination of the reports for other years indi- 
cates that the above exhibit is fairly representative, except that the 
expenditure for stone is smaller than the average. In the state^ 
aid roads built from 1894 to 1899, the cost of the broken stone was 
equal to 55 per cent of the total cost of the road, but in later 
years the amount of stone used was decreased. 

391. New York. In the State of New York in 1898, 22 miles of 
state-aid macadam roads were built in six sections, with an average 
cost of 84.0 cents per square yard, the maximum being $1,085 and 
the minimum 64.8 cents. The roads consisted of 4 inches of native 
stone, and 2 inches of trap rock bound with limestone screenings.! 

392. Michigan. In Michigan the average cost of 52 miles of 
water-bound macadam roads is as follows: t 





Average. 




Per Mile. 


PerSq. Yd. 


Broken stone, cubic yards 


1653 

$ 435.85 

2 264.88 

71.80 

1621.91 


313 


OradincT shaoine and draining 


$0 083 


Crushed stone 


0.523 


Culverts 


0.013 


SurfaoinsT including loadinsr and haulins!. 


307 






Total 


$4 394.44 


SO . 925 







393. Missouri. In Missouri the average cost of two-course work 
is as stated in the table at the top of page 223. § 

394. Specifications. The American Society of Municipal Im- 
provements publish specifications for water-bound broken-stone 
roads, printed copies of which may be had for a nominal sum. These 
specifications are changed from time to time as is necessary to keep 
them up to date. 

* Report of Massachusetts Highway Commission., 1898, Appendix C, p. 74-75, 
t Report of New York State Engineer and Surveyor, 1899, p. 37, 
X Engineering and Contracting, \ol. 41 (1914), p. 705, 
§/&jd., Vol.38(1912),p. 14. 



AfiT. 3] 



MAINTENANCE 



223 



Items. 



Quarry rent. 

Quarrying 

Crushing 

Hauling, 1 mile . 

Shaping road-bed 

Spreading material 

Rolling 

Sprinkling 

Superintendence 

Incidentals 

Total, exclusive of interest and depreciation on 
plant, profits, and administration 



Per Sq. Yd. of 
Road Surface. 



$0,013 
0.100 
0.075 
0.075 
0.025 
0.025 
0.013 
0.013 
0.013 
0.013 



$0,364 



Per Cu. Yd. of 
Loose Stone. 



$0.05 
0.40 
0.30 
0.30 
0.10 
0.10 
0.05 
0.05 
0.05 
0.05 



$1.45 



Art. 3. Maintenance 

395. After the road has been properly rolled and the surface 
has been made compact and smooth, it is very desirable that it 
should always be maintained in that condition. Many seem to 
believe that a macadam road is a permanent construction which 
needs no attention after completion; but proper maintenance is as 
important as good construction. 

Formerly much attention and study was given to the causes of 
wear of water-bound macadam roads; and it was needed, for many 
such roads were subjected to a heavy travel, and required great care 
to keep them in usable condition. To maintain the roads in good 
condition it was necessary to make repairs either at frequent intervals 
or continuously, and to add new material as the old was washed off 
or blown away. But the coming of the automobile made neces- 
sary a radical change in the methods of maintenance and con- 
struction of broken-stone roads. With horse-drawn vehicles the 
abrasion of the horses' feet and of the metal tires wore off dust or 
binder to replace that washed off and blown away; but the fast- 
moving low-hung body of the automobile threw more of the road dust 
into the air than horse-drawn vehicles, and hence more of the binder 
was blown away, and besides the automobile made no dust to replace 
that blown away. Further, the action of the wheels of the auto- 
mobile, particularly in starting and stopping and in rounding curves, 
tends to dislodge the stones. 

Therefore the introduction of the motor=driven vehicles radically 
changed the method of maintenance of the broken-stone roads. 
Instead of trying to maintain a water-bound macadam road having 



224 



WATER-BOUND MACADAM ROADS 



[CHAr. vi 



any considerable amount of motor-driven traffic, by adding new 
material to replace that washed oflf and blown away, it became the 
practice to give the surface of such roads a coating of bitimainous 
material, such as tar or asphalt, which prevented the formation of 
dust and also protected the surface from wear. This method of 
treatment is discussed in Chapter IX. 

396. Since the introduction of motor-driven vehicles, the only 
water-bound macadam roads not protected by a bituminous coating 
are those that carry only a small amount of travel, particularly a 
small number of motor vehicles; and hence the maintenance of such 
roads is not of great importance. Therefore the maintenance will 
be considered only briefly. 

397. Raveling. One of the chief evils to be contended with in 
the maintenance of a crushed-stone road is the tendency to ravel, 
i. e., for one stone after another to work loose on the surface. This 
occurs only after a long dry spell or in a road originally deficient in 
binding power, and is more likely to occur on lightly traveled roads 
than on those having heavy traffic. Raveling may take place 
where the wind sweeps away the binding material from the surface, 
or on a steep grade where the water has washed the fine material 
away from between the fragments; and is chiefly due to the picking 
of the horses' shoes, which in a measure is counteracted by the rolling 
action of the wheels. 

Two expedients are employed to prevent raveling. 1. Sprink- 
ling the road with water effectually stops raveling, and causes the 
surface to solidify again. This is the most common remedy on city 
streets and suburban roads — where water is usually convenient and 
plentiful. For a further discussion of Sprinkling, see § 401. 2. 
A thin coating of coarse sand is very effective in preventing ravehng. 
Ordinarily on country roads a layer half an inch thick is sufficient. 
Unless the season is very dry or the road is unusually exposed to the 
wind, a single application will be enough for one season. 

398. Ruts. Next after raveling, the tendency to form ruts is 
the most serious evil to be contended against in the maintenance of 
crushed-stone roads. Ruts are due either (1) to a greater wheel 
load than the road is capable of standing, or (2) to the use of an 
inferior binding material, as loam, or (3) to tracking. Ruts are most 
fikely to occur in the spring or during a wet time, when the road- 
bed is soft, and are more common on country roads than on city 
streets, since in the latter the frequent changes in direction to avoid 
other vehicles produce a more uniform wear over the whole surface of 



ART. 3] MAINTENANCE 225 

the road. However, a street-car track in a broken-stone road pre- 
vents the distribution of traffic uniformly over the entire surface and 
greatly increases the tendency to form ruts. 

After ruts appear the only remedy is to fill them either with 
new material or by picking down the sides of the ruts and raking 
the loosened material into the depression. Usually the la,tter course 
is the wiser, particularly on a new road. Frequently the tendency 
to form a rut may be effectually arrested by sweeping into it the loose 
detritus from the adjacent parts of the road. If the road surface 
is compact and hard, it may be necessary to loosen the bottom and 
sides of the rut before adding new material, so that the new will 
thoroughly unite with the old. The new material should be of the 
same character as the old, as otherwise the surface will wear unequally 
and become rough. 

399. Patching. Formerly much attention was given to the 
patching of macadam roads to keep the surface free from ruts and 
depressions (see pages 253-57 of the former editions of this treatise) ; 
but the only water-bound macadam surfaces now in use are those 
having a comparatively small amount of travel, and therefore the 
repair of such roads is a comparatively simple matter. 

When new stone is added, the old surface should be loosened to 
insiu-e that the new stone will unite with the old. The patch should 
be rounded rather than square cornered. Care should be taken to 
leave no place where water may lodge. When new, the patch should 
be a httle higher than the adjoining surface. The stone employed 
in patching should be a little smaller than that used in the original 
construction. It is better to lay the stone in two thin courses than 
in a single thick one, and allow the first to become consolidated 
before the second is added. Ordinarily, in applying patches in^thin 
coats over small areas it is unnecessary to use binding material, since 
the road usually has enough detritus to fill the interstices of the new 
stone. If laid in damp weather, when the surface of the road is soft, 
there is usually no difficulty in getting a layer one-stone thick to 
consolidate without any binding material. If the patch is small 
and thin, it will usually not be necessary to tamp or roll it. 

When the surface of the road has become uneven and rough, 
and when the broken stone is thick enough not to require much new 
material, the top of the road is loosened, re-graded, and re-rolled. 
The loosening is usually done by running over the road, one or more 
times, with a steam stone-road roller having spikes in the rear wheels, 
or by breaking up the surface with a scarafier, — a cros^ between a plow 



226 



WATER-BOUND MACADAM ROADS 



[chap. VI 



and a harrow. After the crust is broken up, the surface is leveled 
off by the use of a harrow and hand shovels and rakes; and then it is 
sprinkled and rolled as in the original construction. Usually no new 
binding material is required, the detritus from the old road being 
sufficient. 

400. Rolling. In the spring after the frost goes out, the road 
bed is soft and porous; and a thorough rolling with a steam roller 
at this time, before the subgrade is dry, is one of the best and cheap- 
est methods of keeping a macadam road in good condition. Just 
before this rolling is the time to add a little fresh surface material, 
here and there, as may be needed to fill up slight depressions. 

401. Sprinkling. Moisture is necessary to preserve the cement- 
ing power of the binding material, and also to prevent an excessive 
removal of dust by the wind; and therefore sprinkling to the extent 
required to prevent these injuries is an advantage. The water 
should be applied in a fine spray, and not be allowed to run in streams 
on the road; that is, several light sprinklings are better than a single 
flooding. If sprinkled too heavily or too often, the road is softened 
and breaks up easily. 

Sprinkling is usually employed on park drives and city streets, 
where it is generally conceded to be true economy, without taking 
into consideration the prevention of dust; but it never was much 
used on rural roads on account of the expense, and the introduction 
of bituminous coatings as dust preventatives has entirely done 
away with sprinkling as a road preservative. 

402. For a discussion of sprinkling with water, oil, etc., see 
§ 325-31 under Gravel Roads. 

For a discussion of bituminous coatings for macadam roads, 
see Art. 1 and 2 of Chapter IX. 

403. Cost of Maintenance. The introduction of automo- 
biles greatly increased the cost of maintaining water-bound mac- 
adam roads (see § 395). Data on the cost of maintaining water- 
bound roads before the advent of motor-driven vehicles are now of 
little or no value ; and there are almost no data on the cost of main- 
tenance of such roads where the amount and character of the travel is 
known. 



CHAPTER VII 
PORTLAND-CEMENT CONCRETE ROADS 

406. Definitions. The wearing coat of a concrete road is a 
layer of portland-cement concrete. The word concrete ordinarily 
means a mass of pebbles or broken stone bound together into a solid 
mass by hydraulic cement ; and the word cement in engineering liter- 
ature ordinarily means hydrauhc cement, and in recent years it 
usually means portland cement. Until recently the type of road 
considered in this chapter was called a concrete road. However, 
the preceding meanings do not now apply in discussions concerning 
roads and pavements. Recently a form of construction has been 
introduced in which the pebbles or fragments of broken stone are 
held together by bituminous cement instead of hydraulic cement; 
and therefore to prevent the possibility of misunderstanding it is 
wise to employ the terms portland-cement concrete road or simply 
portland-concrete road, and bituminous-cement concrete roa.d or 
simply bituminous-concrete road, to designate these two types. 

407. History. Except three comparatively small sections con- 
structed earlier, concrete was not used for road surfaces until the 
earty years of this century. In 1909 there were in this country less 
than a half million square yards; but in 1916 there were laid in this 
country 24 million square yards of such road surfaces, an increase of 
forty-eight times in 7 years. At present about 50 per cent of such 
surfaces are on rural roads, and about 25 per cent each on streets and 
alleys. 

Akt. 1. The Materials 

408. The concrete is composed of portland cement, sand or stone 
screenings, and pebbles or broken stone. The sand or stone screenings 
are often called the fine aggregate, and the pebbles or the crushed 
stone the coarse aggregate. 

409. Cement. For a discussion of the characteristics of the 

227 



228 



PORTLAND-CEMENT CONCRETE ROADS 



[chap VII 



different types of hydraulic cement and of the methods of testing the 
same, see pages 54-83 of the tenth edition of the author's Treatise on 
Masonry Construction.* The only form of hydrauHc cement used 
in concrete roads is portland cement. 

It is almost universally specified that the cement shall meet the 
requirements of the latest standard specifications of the American 
Society for Testing Materials, which also have been adopted by all 
of the national engineering associations. Printed copies of these 
specifications can be had of the above Society for a nominal sum; 
and they have been republished by various organizations. 

410. Fine Aggregate. For an extended discussion of the 
characteristics and requirements of sand and screenings for making 
concrete and the method of testing each, and also for a discussion 
of the relative merits of sand and screenings, see pages 85-97 of 
the tenth edition of the author's Treatise on Masonry Construc- 
tion.* 

411. Sand vs. Screenings. The finer particles screened out of 
the broken stone are sometimes used in concrete instead of sand; 
and there is much discussion as to the relative merits of sand and 
screenings. Experiments show that if all conditions are the same, 
the screenings make slightly stronger mortar; but in practice it has 
been found nearly impossible to exclude dust from the stone screen- 
ings, particularly if the stone is soft (as is most limestones) or if the 
screenings get wet before being screened, and hence in practice mor- 
tar or concrete made from screenings is not usually as strong as that 
made of sand of the same degree of fineness. For these reasons 
many engineers prohibit the use of stone screenings. 

412. The specifications for the fine aggregate recommended by 
the 1916 National Conference on Concrete Road Building are as 
follows : 

"The fine aggregate shall be natural sand or screenings from hard, tough, 
durable crushed rock or gravel; and shall consist of quartzite grains or other 
equally hard material graded from fine to coarse with the coarse particles pre- 
dominating. When dry it shall pass a screen having four meshes per hnear inch, 
and not more than 25 per cent shall pass a sieve having fifty meshes per 
linear inch, and not more than 5 per cent shall pass a sieve having one hundred 
meshes per linear inch. It shall not contain vegetable or other deleterious mat- 
ter, nor more than 3 per cent by weight of clay or loam. Routine field tests shall 
be made on the fine aggregate as dehvered. If there is more than 5 per cent of 



* A Treatise on Masonry Construction, by Ira O. Baker. 
Wiley & Sons, New York City. Tenth Edition, 1909, 



745 pages, 6X9 inches. John 



ART. 1] MATERIALS 229 



clay or loam by volume settled after one hour's shaking in an excess of water, 
the material represented by the sample shall be held pending laboratory tests. 

"The fine aggregate shall be of such quality that mortar composed of one 
part Portland cement and three parts fine aggregate, by weight, when made into 
briquettes, shall show a tensile strength (at seven and twenty-eight days) 
equal to or greater than the strength of briquettes composed of one part by weight 
of the same cement and three parts standard Ottawa sand. The percentage of 
water used in making the briquettes of cement and fine aggregate shall be such 
as to produce a mortar of the same consistency as that of the Ottawa sand bri- 
quettes of standard consistency." 

413. Coarse Aggregate. For a discussion of the requisites 
of gravel and broken stone for concrete, see pages 97-103 of the 
tenth edition of the author's Treatise on Masonry Construction. 

414. Gravel vs. Broken Stone. There is difference of opinion 
as to the relative merits of gravel and broken stone for concrete. 
The elements to be considered are the strength, density, and cost of 
the concrete. 

Gravel concrete has only about 80 to 90 per cent of the strength 
of broken-stone concrete. 

Experience shows that gravel concrete is more easily compacted, 
and has fewer cavities than broken-stone concrete; and hence gravel 
concrete is denser and more waterproof. 

As a rule, the first cost of gravel is less than that of broken stone, 
and the former is considerably easier to handle. 

415. However, since gravel is liable to contain so much clay or 
loam as to materially reduce the strength of the concrete, some 
engineers for this reason alone prefer broken stone to gravel. Even 
though only portions of the gravel are naturally dirty, or even though 
only portions of it are likely to contain an undue amount of the strip- 
ping, some engineers, owing to the greater care required in inspection 
and to the uncertainty of eliminating all dirty gravel, prefer broken 
stone to gravel. 

416. The Specifications for the coarse aggregate recommended by 
the 1916 National Conference on Concrete Road Building are as 
follows : 

"The coarse aggregate shall consist of clean, hard, tough, durable crushed 
rock or pebbles graded in size, free from vegetable or other deleterious matter; 
and shall contain no soft, flat or elongated particles. The size of the coarse 
aggregate shall be such as to pass a U-inch round opening, and shall range from 
1| inches down; and not more than 5 per cent shall pass a screen having four 
meshes per linear inch, and no intermediate sizes shall be removed. 

"Crusher-run stone, bank-run gravel, or artificially prepared mixtures of 
fine and coarse aggregate shall not be used." 



230 PORTLAND-CEMENT CONCRETE ROADS [cHAP. Vll 

417. Theory of Proportions. The whole theory of the 

proper proportions for concrete is comprised in two laws as follows: 

1. For the same fine aggregate and the §ame coarse material, the 
strongest concrete is that containing the greatest per cent of cement 
in a unit of volume. 

2. For the same per cent of cement and the same aggregates, the 
strongest concrete is made with that combination of fine and coarse 
aggregate which gives a concrete of the greatest density. 

The first law is almost self-evident, and concerns the relative 
richness of the concrete. Experiments have show^n this law to be 
almost mathematically exact. 

The second law is very important, and concerns the qualities of 
the fine and coarse aggregates. The second law is equivalent to say- 
ing that the cement should fill the voids of the sand, and that the 
resulting mortar should fill the voids of the coarse aggregate. If the 
cement does not fill the voids of the sand, or if the mortar does not 
fill the voids of the coarse aggregate, the concrete will obviously be 
less dense than though the voids were just filled. If the paste is more 
than enough to fill the voids in the sand, or if the mortar is more than 
enough to fill the voids in the coarse aggregate, the concrete will be 
less dense than though the voids were just filled; since both the paste 
and the cement mortar have a less density than ordinary concrete; 
and hence the strength due to the increased amount of cement may 
be neutralized by the decrease in density, but the possibihties of 
this depend upon the plasticity of the mortar, the amount of tamp- 
ing, the character of the sand and the stone, and the gradation of 
the sizes. Experiments and experience have shown this law to be 
almost mathematically exact. 

418. Methods of Proportioning. There are four methods in 
more or less general use for proportioning concrete, w^hich may be 
briefly designated as follows: (1) by arbitrary assignment; (2) 
by voids; (3) by trial; and (4) by sieve-analysis. These methods 
will be considered separately in the above order. 

419. Proportioning by Arbitrary Assignment. This is the least 
scientific method of proportioning, it virtually assumes the relations 
as a matter of judgment, without much, if any, consideration of the 
character of the aggregate; that is, the proportions are assigned 
without any reference to the fineness or coarseness of the sand and the 
stone, or to the gradation of the sizes of each. 

420. Proportioning by Voids. To determine the best propor- 
tions for any particular sand and aggregate, find the per cent of voids 



ART. 1] MATERIALS 231 

in the sand and in the stone, and use enough cement paste to fill the 
voids in the sand and enough mortar to fill the voids in the coarse 
aggregate. Owing to the errors in using this method, and particu- 
larly in getting the cement paste to fill the voids of the sand and the 
mortar to fill the voids of the stone, this method is not very prac- 
tical. 

421. Proportioning by Trial. The second law in § 417 leads to a 
simple method of finding the best relation of the sand and the stone. 
According to that law that combination of sizes of sand and stone 
which with a constant quantity of cement gives the least volume of 
concrete is the best. 

To apply this method procure a vessel of uniform cross section, 
say a cylinder, 10 or 12 inches in diameter and 12 or 14 inches deep, 
its strength being such that its volume will not be changed in tamping 
it full of concrete. Weigh out a unit of cement, and any number of 
units of sand, say two, and also weigh out any number of units of 
broken stone, say five, taking care that the quantities are such that 
when the ingredients are thoroughly mixed and placed in the cylinder, 
the mixture will fill it only partly full, — say three quarters full. 
Make a concrete of any desired consistency by mixing the cement, 
sand and stone with water on a sheet of steel ; tamp the concrete into 
the cylinder leaving the upper surface smooth and horizontal, and 
then measure the depth of the concrete from the top of the cylinder. 
Next empty the concrete from the cylinder, clean it and the tools; 
and then make another batch with different proportions of sand and 
stone, keeping the quantity of cement and the plasticity of the con- 
crete the same as before. If this batch when tamped into the cylin- 
der gives a less volume of concrete, this proportion is better than the 
first. Continue the trials until the proportion has been found which 
will give the least depth in the cylinder. 

422. Proportioning by Sieve Analysis.* " Sieve analysis con- 
sists in separating the particles or grains of a sample of any material — 
such as broken stone, gravel, sand or cement — into the various sized 
particles of which it is composed, so that the material may be repre- 
sented by a curve each of whose ordinates is the percentage of the 
weight of the total sample which passes a sieve having holes of a 
diameter represented by the distance of this ordinate from the origin 

* This method of proportioning the sizes of the sand and stone in concrete was devised by 
Wm. B. Fuller, and is described by him in detail on pages 183-215 of Taylor and Thomson's 
Concrete Plain and Reinforced (1909 edition), from which these extracts are taken by permis- 
sion of the authprSi 



232 



PORTLAND-CEMENT CONCRETE ROADS [CHAP. VII 



in the diagram." The line DBKLA, Fig. 73, is a typical sieve- 
analysis curve for crusher-run micaceous-quartz stone; and the line 
OF represents a fine sand. 

^' The objects of sieve-analysis as applied to concrete aggregates 
are: (1) to show graphically the sizes and relative sizes of the par- 
ticles; (2) to indicate what sized particles are needed to make the 
aggregate more nearly perfect, and so to enable the engineer to im- 
prove it by the addition or substitution of another material; and (3) 
to afford means for determining the best proportions of different 
aggregates." 

'' The experience which the writer [Fuller] has had and the various 
experiments which he has made indicate that concrete which works 



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Diarnefer of Parf/c/es in Inches 

Fig. 73. — Sieve-Analysis Curve. 



t50 



175 



the smoothest in placing and gives the highest breaking strength for 
a given percentage of cement, is made from an aggregate whose 
sieve analysis, taken after mixing the sand and the stone, forms a 
curve approaching a parabola having its beginning at the zero of co- 
ordinates and passing through the intersection of the curve of the 
coarsest stone with the 100 per cent line, that is, passing through the 
upper end of the coarsest stone curve." In Fig. 73, the parabola 
OCPA represents a theoretically perfect combination of sizes of 
sand and stone all of whose pieces pass a 1 J-inch screen. This curve 
shows, for example, that for the best combination of the above 
materials 93 per cent of the mixture should pass the l^-inch sieve, 76 



i 



ART. 1] MATERIALS 233 

per cent should pass the 1-inch sieve, 54 per cent the J-inch, and so 
on." 

" Where, as in Fig. 73, the materials to be mixed are represented 
by only two curves no combination of which will make a curve as 
close to a parabola as is desirable, there is another limiting condition 
which was brought out by the experiments, viz., that for the best 
results the combined curve shall intersect the parabola on the 40 
per cent line, at C, and that the finer material shall be assumed to 
include the cement." 

423. The curve DBKLA, Fig. 73, may be transformed so that 
it will pass through C, by changing the distances from the top of the 

diagram to the line DBKLA in the proportion -=^ = — = 61 per cent, 

which shows that 61 per cent of the dry materials should be broken 
stone. In a similar manner the line OF is re-plotted in the position 
OJ. The line OJCGA is assumed to represent the best possible 
combination of sizes of this sand and stone. For example, with the 
best possible combination of sizes of this stone and sand, 89 per cent 
would pass the l|-inch sieve, 67 per cent would pass the 1-inch sieve, 
46 per cent the i-inch sieve, and so on. 

" The proportion of cement to be used to give the required 
strength of concrete must always be assumed; and in this example 
it will be assumed that the cement is to constitute one eighth of the 
dry materials (measured before the sand and stone are mixed together) , 
which will make the cement one ninth or 11 per cent of the total dry 
materials. Since the diagram shows that the sand and cement are 
to constitute 39 per cent of the dry materials, the sand must then be 
39-11=28 per cent." 

" The proportions of concrete for 1 part cement to 8 parts of 
sand and stone, measured separately, then are: 11 per cent cement, 
28 per cent sand, and 61 per cent broken stone, or 1 : 2.5 : 5.5 by 
weight. If the proportions are required by volume and the relative 
weights of the sand and the stone differ from their relative volumes, 
the proportions should be corrected accordingly." 

424. " An important feature of the sieve-analysis curves is that 
they show how the materials may be improved by adding or sub- 
tracting some particular size. For example, if the stone repre- 
sented by the curve DBKLA in Fig. 73 had contained more pieces 
0.5 and 1.0 inch in diameter, its curve would have more nearly ap- 
proached the parabola in the region SG. If a stone giving the line 
DRHA were used, the ratio for transforming the line to make it 



234 PORTLAND-CEMENT CONCRETE ROADS [CHAP. VH 

pass through C would be -^^ = 7^7 = 66 per cent, which shows that with 

the assortment of sizes of broken stone represented by this hne the 
best concrete is made by using 66 per cent of broken stone. For a 
1 : 8 mixture as before, the proportions would be 11 : 23 : 66, or 
1:2: 6, — a cheaper, stronger, and denser concrete than that made 
with the stone represented by the line DBKLA." 

For further details concerning this method and for later slight 
modifications in the form of the ideal sieve-analysis curve, see Taylor 
and Thompson's book mentioned above or the author's Treatise on 
Masonry Construction.* 

^' This method affords a means of determining the best propor- 
tions in which to mix the fine and coarse aggregate, and also shows 
how the aggregate may be improved by adding or subtracting some 
particular size. Sieve analyses can be made from time to time as 
the work progresses to see whether or not the sizes of the aggregate 
have changed; and if the sizes have changed, the proportions can be 
varied to secure the most economical and the densest concrete. 
In a work of any magnitude the greater labor required in determining 
the proportions by sieve-analysis curves is hkely to be justified by 
the better quality, or the less cost, of the concrete; and the extra 
labor required to make sieve analyses during the progress of the work 
will be worth all it costs because of the better control of the propor- 
tions of the concrete. 

" To secm*e the maximum benefit of this method of proportion- 
ing, it is necessary to screen the aggregate to several sizes and then 
combine them in the proportions indicated by the sieve-analysis 
curve. As to whether or not the increased cost of screening and 
proportioning would be justified by the saving of cement, depends 
upon the magnitude of the work and other conditions. The following 
example illustrates the possibilities: 

'' The ordinary mixture for water-tight concrete is about 
1 : 2J : 4 J, which requires 1.37 barrels of cement per cubic yard of 
concrete. By carefully grading the materials by the methods of 
sieve analysis the writer [Fuller] has obtained water-tight work with 
a mixture of about 1 : 3 : 7, which requires only 1.01 barrels of 
cement per cubic yard of concrete. This saving of 0.36 barrel is 
equivalent, with portland cement at $1.60 per barrel, to $0.58 cubic 

* For an explanation of the advantages of plotting sieve-analysis curves on logarithmic 
cross-section paper, and of an ingenious use of the method, see Engineering and Contracting, 
Vol. 47 (1917), p. 230. 



ART. 1] MATERIALS 235 

yard of concrete. The added cost of labor for proportioning and 
mixing the concrete because of the use of five grades of aggregate 
instead of two, was about $0.15 per cubic yard, thus effecting a net 
saving of $0.43 per cubic yard." 

425. Data for Estimates. Portland Cement. Portland ce- 
ment, which is now practically the only cement used in engineering 
construction, is usually shipped in cloth bags containing 94 lb. each. 
The cement is usually sold by the barrel, which is considered as foiu* 
bags. In computations involving the proportions for concrete, a 
bag is usually considered as containing one cubic foot of packed 
cement. 

Until the disturbance of prices by the Great European War the 
price of portland cement at any place east of Omaha, Nebraska, 
was from $1.50 to $1.75 per barrel in cloth bags, the bags being 
charged at 10 cents each and undamaged bags being returnable at 
that price. 

426. Sand and Gravel. Before the Great European War the 
price of washed, screened, and graded sand at the pit was about 25 
cents per ton; and of washed, screened, and graded gravel, about 35 
cents per ton. The freight was about 47 to 48 cents per ton per 100 
miles in each case. 

427. Broken Stone. Before the disturbances of prices by the 
Great European War, the price of crushed limestone, screened 
and graded, f.o.b. the quarry, was about 55 cents per ton; and the 
freight was about 47 to 48 cents per ton per 100 miles. Limestone, 
graded and loaded into a freight car weighs about 2500 lb. per cubic 
yard. 

The cost of crushed trap f.o.b. the quarries in New Jersey for 
several years previous to 1900, was 40 to 50 cents per ton (about 50 
to 62 cents per cubic yard) ; but in that year the price was increased 
nearly 50 per cent. In Massachusetts, the cost of broken trap on 
cars at the end of the railroad transportation, varies from $1.10 to 
$1.60 per ton (about $1.32 to $1.93 per cubic yard). In Boston, the 
cost of crushed granite delivered on the streets is $1.65 to $1.90 per 
ton. In Montreal, syenite delivered on the streets costs an average 
of $1.15 to $1.20 per ton. 

428. Ingredients for a Cubic Yard. Table 28, page 236, shows 
the quantities of cement, sand, and stone required for a cubic yard 
of concrete of different proportions, using three grades of broken 
stone or gravel. The concrete was mixed wet but not soupy; and 
was also mixed very thoroughly. If it had been mixed drier or less 



236 



PORTLAND-CEMENT CONCRETE ROADS [CHAP. VII 



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ART. 1] MATERIALS 237 

thoroughly, it would have been less dense, and consequently less 
quantities of materials would have been required to make a yard. 

Data like that in Table 28 are affected by the fineness of the 
cement, the fineness and dampness of the sand, the kind and coarse- 
ness of the stone, the proportions of the several sizes of sand grains 
and stone fragments, the thoroughness of the mixing, the amount of 
tamping, etc.; and different experimenters have obtained widely 
different results. Most experimenters obtain a less quantity because 
the concrete is mixed drier and entrains more air, and hence is less 
dense. 

429. Fuller's Rule. The following rule, devised by Wm. B. 
Fuller,* gives the quantities of cement, sand, and stone required to 
make a cubic yard of concrete; and is fairly representative of all 
classes of materials. This rule is valuable because it is so simple 
that it can be carried in the memory. 

c = number of parts of cement. 

s = number of parts of sand. 

g = mmiber of parts of gravel or broken stone. 

C = number of barrels of packed portland cement required for 1 

cubic yard of concrete. 
S = number of cubic yards of loose sand required for 1 cubic yard 

of concrete. 
G = number of cubic yards of loose gravel or broken stone required 

for 1 cubic yard of concrete. 



c + s + g' 



S^CXsX—; 
G^CXgX^^, 

" If the coarse material is broken stone screened to uniform 
size, it will contain less solid matter in a given volume than average 
stone, and hence about 5 per cent should be added to quantities of all 
three ingredients as computed by the above rule. On the other hand, 
if the coarse material is well graded in size, about 5 per cent may be 
deducted from all of the quantities." 



* Taylor and Thompson's Concrete Plain and Reinforced, Second Edition, p. 16. 



238 PORTLAND-CEMENT CONCRETE ROADS [cHAP. VII 

The preceding formulas are sometimes modified by changing the 
constants 11 and 3.8. For example, one engineer substitutes 9.5 
for the 11, and 4 for the 3.8. 

Art. 2. The Construction 

431. Drainage. The drainage of the road-bed of a concrete 
road or pavement is of vital importance. If the subgrade is not well 
drained, there is danger that after the concrete is laid, the drying of 
the soil under the edges of the concrete may permit the pavement to 
settle and thus cause longitudinal cracks on the surface. Further, 
if the subgrade is not well drained, there is a possibility that the frost 
may lift the edges of the concrete roadway and cause a longitudinal 
crack, — at least on the lower side. With some forms of roads a crack 
in the surface will heal under travel; but a crack in a concrete pave- 
ment not only can not heal under travel, but will continually enlarge. 
There is no part of the work of the construction of a concrete road or 
pavement that is more worthy of intelligent care and painstaking 
labor than the preparation of the subgrade; and the slight addi- 
tional cost necessary to insure good results is abundantly justifiable. 

If the soil is sandy, there is a probability that the natural under- 
drainage is sufficient for the purpose. 

If the soil is only moderately retentive, a shallow longitudinal 
ditch should be constructed just outside of the edge of the concrete 
slab. The ditch should extend about 8 or 10 inches below the sur- 
face of the road-bed, i. e., below the bottom of the concrete slab; and 
should be filled with coarse gravel or broken stone. From this longi- 
tudinal ditch short transverse trenches should be dug across the 
shoulder to the ditch, at the side of the roadway. These transverse 
trenches should have a grade sufficient to permit them to carry the 
water promptly and completely to the side ditch. In particularly 
retentive soil, these transverse trenches should not be placed more 
than 50 feet apart. On the level stretches, these transverse trenches 
should be practically at right angles to the direction of the road; 
but if the road is on a grade, they should make an acute angle with 
the roadway, the amount of this angle depending upon the grade of 
the road. These lateral ditches should be filled level full with broken 
stone or coarse gravel to a point at least a little beyond the outer 
edges of the shoulders and preferably nearly to the bank of the ditch 
at the side of the roadway. 

If the soil is so retentive that the underground water level is likely 



ART. 2] 



THE CONSTRUCTION 



239 



to rise within a foot or so of the surface, then a farm tile should be laid 
on one or both sides of the paved portion. For a discussion of the 
purposes of underdrainage and the method and cost of laying the 
tile, see § 114-24 of Chapter III, — Earth Roads. For a discussion of 
the subject of Side Ditches, see § 125-28. 

432. V-Drains. Some engineers employ what is usually called 
a V-drain, Fig. 74. The subgrade is excavated to a depth below 



Concre i^ y^aring C ogf 




Fig. 74.— The V-Dkain. 



the base of the concrete slab of 12 to 18 inches at the center and 4 to 
6 inches at the side, and this trench is filled with loose stone. 
The sizes of the stones are usually limited as follows: the largest 
the equivalent of a 6-inch cube, and the smallest a 2-inch fragment. 
The largest stones are placed in the bottom of the trench, and no 
3-inch stone is allowed within 2 inches of the upper surface of the 
stone in the trench. After the trench is filled with stones, it is usually 
rolled with a self-propelling roller, and any depressions that appear 
are filled with stones. 

This form of drain ordinarily costs 50 to 60 cents per linear foot, 
and is of doubtful economy, unless where bowlders or loose stones 
abound on or near the road, or where the road is on very wet and 
retentive soil. 

433. Preparing the Subgrade. The fundamental require- 
ment is that the subgrade shall at all times be of uniform density, 
so that it will not settle imevenly and cause cracks in. the concrete 
surface. 

434. Before the grading is begun, or at least before it is com- 
pleted, the curbs (Chapter XIV) are built, or the side forms (§ 448) 
are set, to serve as guides in bringing the subgrade to the proper 
surface. 

435. On Virgin Soil. All brush, trees, stumps, and large roots 
for a width of 25 feet on each side of the center line of the proposed 
roadway, should be cut off and be removed from the limits of the 
right-of-way.* The road should be grubbed for the full width of the 

* If the pavement is to be mpre tb^o 15 feet wide, this quantity is to be proportioiially 
greater. 



240 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. VII 



excavation, and no stumps or large roots should be left within these 
limits except when a fill of more than 5 feet is called for on the plans, 
in which case all stumps should be cut off to within 12 inches of the 
original ground level. Stumps on the cleared portion not within the 
grubbed limits, should be cut off to within 12 inches of the original 
ground level. Stumps on the cleared portion not within the grubbed 
limits, should be cut off not more than 2 feet from the ground. 

All soft or spongy spots and all vegetable matter should be 
removed, and the space be re-filled with suitable material. It is not 
wise to put any dependence upon the ability of the concrete slab to 
bridge soft spots. After the subgrade has been brought to the proper 
surface, it should be rolled with a 3-wheel 10-ton self-propelling roller 
to disclose any soft spots. Any depressions discovered in rolling 
should be filled and be re-rolled until no depressions appear. The 
rolling should be continued until the roller leaves no material track 
or depression. However, clean dry sand can not be consolidated by 
rolling; and some plastic clay can be rolled too much. 

After the grading is completed, if the natural lay of the ground 
is such that there are sumps or pockets w^hich hold water, or if such 
sumps or pockets are made during the progress of the work, they 
should be thoroughly drained. 

436. On Earth Road. If the concrete road or pavement is to be 
constructed upon virgin soil, that is, if it is not to be constructed 
on an old road-bed, the precautions described above are sufficient to 
secure a reasonably good foundation. But if the pavement is to be 
constructed upon an old road-bed of any kind, great care must be 
taken in preparing the subgrade. The old road-bed is likely to be 
more compact in the center than at the sides; and consequently 
there is danger that the pavement will settle more at the sides than 
at the center, and therefore will crack longitudinally. Further, it is 
likely that the traveled way of the old road will not at all places be 
central under the new pavement; and consequently the latter will 
settle unevenly and crack. 

When the subgrade is an old roadway, since the roller is likely to 
balance upon the more compact central core and therefore not 
consohdate the soil at the side of the old roadway, it is not sufficient 
to roll the subgrade longitudinally. In extreme cases it may be 
necessary to plow the old road-bed and then harrow it, and finally 
consolidate the entire new road-bed with the roller. 

437. On Gravel or Macadam Road. Not infrequently a concrete 
slab is constructed on an old gravel or macadam road. There is 



ART. 2] THE CONSTRUCTION 241 

considerable difference of opinion as to the wisdom and the method 
of utihzing the old road. The objections and difficulties are that the 
old road usually has too much crown; the surface is full of holes; the 
old road often has an undesirable profile; and the old road is narrower 
than the new one, and consequently the sides are likely to settle and 
crack the concrete slab longitudinally. On the other hand, the old 
road is already in place, is usually well consolidated, and a careful 
investigation should be made to determine whether it can be econom- 
ically used. 

The first thing is to establish a grade line for the subgrade. This 
may require the cross sectioning of the old road at frequent intervals, — 
perhaps each 50 or 100 feet, depending upon the condition of the sur- 
face and the regularity of its profile. After having established a 
grade Une, it is usually necessary to scarify the old road in places to 
remove the high spots. The low places should be filled with gravel 
or stone to avoid an excessive depth of concrete. The subgrade is 
then rolled; and if necessary, the low places are again filled and 
again rolled. The permissible degree of variation of the subgrade 
from the proposed contour depends upon the relative cost of the 
labor required in finishing and of the concrete required to fill the low 
places. 

It is particularly important that the side forms for the concrete 
(see § 448) should be set up, or that the curbs should be built, before 
the old road is scarified, so they may carry the templet used as a 
guide in re-shaping the old road. 

If the old road is narrower than the new, or not central under it, 
great care must be taken in consolidating the soil at the edge of the 
old road. These edges should be covered with gravel or broken stone 
and be rolled until they are firm and solid. 

438. Cross Section of Subgrade. The cross section of the sub- 
grade is made either flat or crowned to conform to the finished sur- 
face of the concrete. The former seems to be the better and more 
common. It is claimed that experience shows that a pavement hav- 
ing a flat subgrade is less likely to crack longitudinally. No entirely 
satisfactory reason for this has been given; but possibly it is due to 
the greater tendency of the two portions to separate when the sub- 
grade is crowned. 

439. One vs. Two-Course Pavements. Usually the con- 
crete is laid in one course at a single operation ; but sometimes, when 
material suitable for the wearing surface is expensive, and when local 
but less suitable material is much cheaper, the concrete is laid in two 



242 PORTLAND-CEMENT CONCRETE ROADS [CHAP. VII 

courses, the lower one of the poorer and cheaper material. The 
lower course is usually also a little leaner and the top course a little 
richer than for a one-course pavement. At times such construction 
may be economical. 

On the other hand, the two-course work is objectionable for the 
following reasons: 1. It is difficult to keep the two classes of material 
separate. This is more serious on a narrow rural road than on a wide 
city pavement. 2. There is a possibility of not securing a good union 
between the two courses. 3. If the lower course is leaner, it will 
absorb water from the subgrade and expand, while the top course 
is likely to dry out and contract; and consequently the two are likely 
to separate. 4. The bottom course absorbs water and expands, and 
is likely to produce a longitudinal crack. 

Good two-course pavements have been laid; but they require 
more labor and greater care in construction. Statistics show that a 
little less than 30 per cent of all concrete roads and pavements are two- 
course work. 

All the discussions that follow relate to one-course work. 

440. If reinforcement is to be used (§ 469), it is necessary to lay 
the concrete in two courses and place the reinforcing net between 
them; but the same mixture is ordinarily used for both courses, 
and hence such construction is not usually classed as two-course 
work. 

441. Cross Section of Pavement. The cross section of the 
concrete slab depends upon its width and thickness, and upon the 
crown of its upper surface. 

Fig. 75 shows the cross sections recommended by the 1916 
National Conference on Concrete Road Construction, for cuts 
and for fills. For the recommendations of a committee of the 
American Society of Civil Engineers concerning crown, see Table 16, 
page 65. 

442. Crown of Surface. In determining the proper crown 
for a concrete road surface, a distinction should be made between a 
country road and a city street. The former need be crowned only 
enough to afford lateral drainage, particularly after the middle is 
worn down somewhat; while on a city street with side curbs, the 
crown should be enough to prevent an undue portion of the pave- 
ment from being covered with water during a rain. 

The only advantage in crowning a road surface is to secure surface 
drainage, and with perfect work a very small crown would suffice. 
An excessive crown drives travel to the middle of the road, and con- 




ART. 2] 



THE CONSTRUCTION 



243 



sequenjbly does not distribute the wear uniformly over the pavement; 
therefore the less the crown the better, provided good surface drain- 
age is secured. Some crown is necessary on account of (1) inev- 
itable imperfections in finishing the surface, (2) the accumulation of 
leaves, twigs, straws, etc., on the surface, and (3) the wear of the 
pavement. 

443. The crown used in practice for concrete roads without 
curbs, varies from ^ to g^ of the width, without much tendency 




Section on Hll 

. /Ire ofCirc/e, \ / ^f^^^^^M 



MzWrnm 




Sect/on on Lei/el or /n Cut 

"tV" DenofGS IV/c/fh of Pbyemenf 
Fig. 75. — Cross Sections for Concrete Roads. 



to group withir any smaller limits. For concrete pavements with 
curbs the crown employed in practice varies from ^ to -^^-^ of the 
width, the intermediate values being used about equally. The 
National Conference on Concrete Road Building recommends a 
crown of ^Jo"- 

444. Super-elevation on Curves. For a discussion of this subject, 
see § 90. 

445. Maximum Grade. For a discussion of the general sub- 
jects of maximum grades, see § 79-85; and for the recommendations 
of a committee of the American Society of Civil Engineers concerning 
maximum grades, see Table 15, page 57. The above committee 
recommends 8 per cent as the permissible maximum; but numerous 
examples could be cited of concrete surfaces on steeper grades. For 
example, Sioux City, Iowa, lays concrete on grades up to 16 per cent, 
and Mankato, Minn., on 14.3 per cent. 



244 PORTLAND-CEMENT CONCRETE ROADS [CHAP. VII 

446. Width. For a general discussion of the width of the im- 
proved portion of a road, see § 95-6. Both the 1914 and the 1916 
National Conference on Concrete Road Building recommended a 
width of concrete of 10 feet for a single-track road, and 18 feet for a 
double-track road; and that for roads 18 feet or more in width, it is 
not necessary to harden the shoulders by applying gravel or broken 
stone. For a consideration of extra width on curves, see § 97. 

447. Thickness of Concrete. The proper thickness depends 
to some degree upon the climate, the width of the slab, the character 
of the soil, the thoroughness of both the surface and the under- 
drainage, the degree of consolidation of the subgrade, the propor- 
tions and quality of the concrete, the character of the workmanship 
of every part, the care employed in curing the concrete, and the 
amount and character of the traffic. These factors are not of equal 
importance, and the importance of any one item may vary consid- 
erably with local conditions. 

It is not possible to compute the thickness required in any par- 
ticular case; and all that can be done toward determining a working 
rule for the thickness of a concrete road slab, is to accumulate data 
concerning practice. In studying the results of experience, care 
should be taken to consider each of the factors mentioned above. 

As a rule engineers make the thickness more at the middle than 
at the sides; but some engineers prefer a uniform thickness, on the 
theory that traffic is likely to be distributed over the entire surface. 
Apparently the latter overlook the heaving effect of frost, and also 
the effect of wear, which is more at the middle than at the sides. 

In California, part of which state is classed as semi-arid and part 
as arid, the State Highway Conamission has laid many miles of con- 
crete roads 16 and 18 feet wide and only 4 inches thick, which have 
given entire satisfaction. 

In Oregon, a state that is chiefly semi-arid, many miles have been 
built 15 feet wide with a thickness of 5i inches at the sides and 6 J 
inches at the crown, which competent authority pronounces as being 
satisfactory. In 1914 three miles of 16-foot roadway were built in 
which the thickness at the sides was only 4 inches and that at the 
crown only 5 inches, and in 1917 this road was in excellent con- 
dition. 

In the Mississippi Valley, the general practice seems to be to 
make the thickness 6 inches at the side and 7 or 8 inches (usually the 
latter) at the crown. 

448. Side Forms. The concrete is laid between side forms or 



ART. 2] THE CONSTRUCTION 245 

curbs. The former is the custom for rural roads, and the latter 
for city pavements. The forms for curbs or combined curbs and 
gutters will be considered in Chapter XIV — Curbs and Gutters. 
For rural roads, planks or steel channels are set at the edges of the 
concrete slab to retain the concrete, the width of the form boards 
determining the thickness of the slab. The forms are usually set 
before the subgrade is brought to its final surface. The tops of the 
forms are used as guides in finishing the surface of the subgrade, and 
later are used to guide the template in striking off the the top surface 
of the concrete. 

The forms may consist of 2- or 2^-iinch plank or of steel channels. 
The plank forms should be securely held in place by means of stakes 
on the outside driven either to such a depth that their tops are below 
the upper edge of the forms or at such a distance outside of the forms 
as not to interfere with the operation of the template. The planks 
should have a continuous bearing on the subgrade, as otherwise 
they will sag when the concrete is struck oif. Adjoining ends of 
the several planks should be fastened together so as to keep them in 
line. Fig. 76, page 247, shows plank forms in reasonably good posi- 
tion. Fig. 77, page 247, shows plank forms poorly constructed and 
poorly set up. In Fig. 77 notice the space under the bottom of the 
side form; and apparently the forms are not in hne either in the fore- 
ground or the back-ground. 

The steel channels are generally more economical than plank; 
and are easier set, and keep their place better. They are provided 
with telescoping joints, which keep the different sections in line; 
and are hung upon steel stakes previously driven to the right depth, 
which make it easy to place the forms at the desired grade. 

The steel side-forms may be flat and leave a square corner on the 
upper edge of the concrete slab, or they may have a projection that 
will leave a beveled edge. However, if the edge of the concrete slab 
is to be beveled or rounded, it is better to secure this, by the use of a 
finishing tool than by a bevel-edge form. 

449. The Concrete. Proportions. The best proportions for 
any particular materials can be determined only by one or the other 
methods explained in §421 and §422; that is, either by finding by 
trial the proportions that give maximum density and hence maximum 
strength, or by sieve-analysis curves. 

The proportions originally used are 1 : 2 : 3, 1 : 2 : 5, 1 : 3 : 6, 
or 1 : 2| : 7. The efficiency of these proportions can not be known 
unless the gradation of the aggregates is known. 



246 



PORTLAND-CEMENT CONCRETE ROADS [CHAP. VII 



450. The National Conference on Concrete Road Building rec- 
ommends (for the fine and coarse aggregates specified in § 412 and 
§ 416, respectively) 1:2:3. The Ohio Highway Department uses 
1 : 2 : 4; and the Pennsylvania Highway Department 1 : IJ : 3 
or 1 : 2 : 3. The U. S. Office of Public Roads uses 1 : H : 3 for 
gravel or 1 : 1 J : 3 for broken stone. 

451. Mixing. The ingredients should be mixed, preferably in a 
batch mixer, until every fragment of the coarse aggregate is covered 
with mortar and until the concrete is of uniform consistency and 
color. Ordinarily this can not be accomplished unless all of the 
materials are in the drimi for at least 1 minute and the drum is run 
at a rate of not less than 12 or 16 revolutions per minute. The time 
element is as important as the number of revolutions, since time is 
necessary to allow the water to diffuse through the mass. Some 
engineers specify that the concrete shall be turned for IJ minutes. 
Experiments show the following relation between crushing strength 
and the time of mixing.* 

Crushing strength when mixed | minute or 9 revolutions = 1400 lb. per sq. in. 
Crushing strength when mixed 1 minute or 17 revolutions = 1587 lb. per sq. in. 
Crushing strength when mixed 1^ minute or 26 revolutions = 1924 lb. per sq. in. 

The drum must be completely emptied before another batch is 
added. 

452. Fig. 76 shows a typical batch concrete-mixer. In this 
case the concrete is delivered with a bottom-dump bucket. The 
bucket should close tightly so as not to leak. Sometimes the con- 
crete is delivered with a tilting bucket. Again, the concrete is 
delivered through a revolving spout having spiral blades on its 
inside; and sometimes the mixing of the concrete due to its travel 
through the tube is offered as an excuse for decreasing the amount of 
mixing in the drum, but this should not be allowed as in its trip 
through the revolving spout the concrete is mixed but a little. Some- 
times the concrete is delivered by sliding it down a trough; but this 
is undesirable as the tendency is to mix the concrete too wet, so it 
will slide freely. Fig. 77 shows a concrete mixer delivering the 
wearing coat of a two-course concrete road through a gravity spout. 
Apparently the mixture is much too wet. 

The concrete is sometimes transported in wheel-barrows or bug- 
gies; but this is objectionable as in the transportation, particularly if 



Engineering News, Vol. 75 (1916), p. 768. 



ABT. 2] 



THE CONSTRUCTION 



247 



the distance is more than 100 feet or if the concrete is quite wet, the 
coarse aggregate settles to the bottom, and the thoroughness of the 
mixing is destroyed. 

453. Batch mixers are made in various capacities from 6 to 60 
cubic feet of concrete; but only those having a capacity from 6 to 30 
cubic feet, a 1- to 5-bag mixer, are used in rural-road or city-pave- 
ment work. A one-bag or two-bag mixer is the most common, as it is 
practically impossible in road work to get the material to a larger 
mixer fast enough to keep it going economically. 

The latest models of batch mixers have a loading skip, a device for 
regulating the time of mix, and an automatic water tank (Fig. 76). 




Fig. 76. — Concreting Chew at Work. 



Fig. 77. — Delivering the Topping op a 
Two-course Concrete Road. 



454. With continuous mixers it is difficult to control accurately 
the proportions and the thoroughness of the mixing. Some con- 
tinuous mixers have devices for automatically measuring the several 
ingredients, and give fairly satisfactory results when intelligently 
operated and kept in good order ; but ordinarily specifications do not 
permit the use of a continuous mixer. 

455. Whatever the type of concrete mixer, it is wise to check 
the proportions occasionally, at last once each day, by noting the 
quantities of the several ingredients used in a certain area of pave- 
ment. Since the volume of concrete produced from stated quanti- 
ties of the ingredients can not be computed accurately, this method 
is a better check upon uniformity than upon the amount of the 
ingredients used; but after a little experience with the particular 
materials and consistency, a real check can be obtained of the 
amount of the ingredients used. 



248 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. VII 




Fig. 78. — Box Wheel-bareow. 



Fig. 78 shows a form of wheel-barrow used on the Allentown 
and Eastern concrete road in Pennsylvania, which secures greater 
accuracy in measuring the ingredients than the usual wheel-barrow 

having a pressed steel bowl with 
fom- curved edges. It can be 
seen at a glance whether the bar- 
row shown in Fig. 78 is full; while 
with the form having four curved 
edges, it is difficult to determine 
whether the barrow contains the 
right quantity. 

456. Hand Mixing. Only a 
few years ago concrete for roads 
and pavements was usually mixed 
by hand; but now it is practi- 
cally all mixed by machine. The 
output per man with a machine 
is usually about 50 per cent more 
than by hand; and the total cost is considerably less by machine 
than by hanS, the exact difference depending upon the thoroughness 
of mixing in both cases, upon the size and type of the machine, and 
upon the amount of work per year done with it. 

457. Re-tempering. The re-tempering of concrete, i. e., the re- 
mixing of concrete that has partially set, should not be permitted 
under any circumstances. 

458. Consistency. The materials should be mixed with sufficient 
water to produce a concrete which will hold its shape when struck off 
with the template. The consist- 
ency should not be such as to 
cause a separation of the mortar 
from the coarse aggregate in 
handling. The tendency is to 
use an excess of water, which 
facilitates the handling of the 
concrete, but also tends to sepa- 
rate the ingredients and greatly 
weakens the concrete. 

Fig. 79 shows the proper con- 
sistency. With less water the concrete will not flow; and with 
more water there will be segregation, the mortar flowing to the 
bottom of the pile. The consistency of concrete is not a sure indi- 




FiG. 79. — Proper Consistency of Concrete, 



J 



ART. 2] THE CONSTRUCTION 249 

cation of its quality, since a given consistency may be produced by 
using more cement and less mixing, or by more mixing and less 
cement, or by adding hydrated lime; but nevertheless the above 
test is a reasonably good one. 

459. Placing. If the subgrade has been rutted up in hauling over 
it, the surface should be restored; and then it should be thoroughly 
sprinkled, but there should be no pools of water when the concrete 
is placed. The thorough sprinkling of the subgrade adds materi- 
ally to the wearing quahty of the concrete, by keeping it from dry- 
ing out too soon. 

Inmiediately after being mixed, the concrete should be deposited 
to the required depth and width. The section should be completed 
to a transverse joint without the use of intermediate forms or bulk- 
heads, or a transverse joint may be placed at the point of stopping 
the work. In case the mixer breaks down, the concrete should be 
mixed by hand to complete the section. 

Where reinforcement is used it should be embedded in the lower 
course of concrete before the concrete has begun to harden; and the 
concrete above the reinforcement should be placed within 20 minutes 
after the placing of the concrete below. 

460. The placing of concrete for roads when the temperature is 
near freezing is not advisable; but if such work is practically un- 
avoidable, the water and the aggregates should be heated before 
mixing, and the fresh concrete should be protected from freezing 
for at last 10 days, if the temperature remains near freezing 
(see § 464). Concrete should never be deposited on a frozen sub- 
grade. 

461. Striking. As soon as placed the concrete should be struck 
off to the established crown and grade by means of a template resting 
on the side forms and moving with a combined longitudinal and 
transverse motion. The concrete should have originally been de- 
posited so high that a little concrete will accumulate in front of the 
template; but this accumulation should not become excessive, and it 
should be kept nearly uniform along the template by removing the 
excess with a shovel and throwing it ahead or where needed along 
the template. As the template approaches a transverse joint most 
of the excess should be removed. 

The template or strike board for a 10- or 12-foot road consists of 
a 2-inch plank 6 or 8 inches wide cut on the under side to fit a crown 
slightly in excess of that of the finished surface, and having handles 
and a shoe to run on the side forms; and for a 14- to 20-foot road. 



250 



PORTLAND-CEMENT C0NCRET3 ROADS 



[CHAP. VII 



two 2- by 10-inch planks spiked together. When the pavement is 
over 20 feet wide a trussed template must be employed.* 

462. A variety of devices have been invented to facilitate the 
striking of the concrete and at the same time^to consohdate the 




Fig. 80. — Hand-Tamping Templates foe Concrete Roads. 




Fig. 81. — Baker Finishing Machine. 



concrete by tamping the surface. One such method consists in first 
using a template that leaves the concrete a little high, particularly 
in the center; and then following with a heavy template having a 



* For detailed drawings of two templates running on rollers and having levers for raising, 
and also being adjustable for different widths of pavements, see Proc. 1916 National Confer- 
ence on Concrete Road Construction, p. 203 and 204. 



ART. 2J 



THE CONSTRUCTION 



251 



handle at each end by which it is hfted and dropped at close inter- 
vals — see Fig. 80. Another device consists of a self-propelling tem- 
plate and tamping machine running upon the side forms. The 
front end of the machine strikes the concrete a little high and the 
rear end tamps it to the right height by an up and down motion 
of a steel plate extending across the pavement. Fig. 81 shows this 
machine. 

463. Finishing. After the concrete is brought to the estab- 
lished grade and crown with the template, the surface is smoothed or 
finished, usually with a wood float, the operator working upon a 
suitable bridge — see Fig. 82. The wood float is better than a 




Fig. 82. — Bridge upon which Finisher Works. 



metal trowel, since the latter gives a polished surface and also tends 
to work a film of neat cement to the surface. 

The time of finishing has a marked effect upon the wearing quality 
of the pavement. The tendency is to finish the concrete too soon 
after placing. The proper time depends upon the weather conditions 
and the wetness of the concrete when placed. The concrete should not 
be finished until it is nearly ready to take the initial set ; and when in 
this condition the surface will contain practically no free water, and 
will be of such a consistency that the wood float will leave distinct 
marks on the surface. All foreign substances, such as sticks, coal, 
lumps of clay, etc., on the surface should be removed before finishing. 

The surface is sometimes stippled with a broom or stiff brush to 



252 PORTLAND-CEMENT CONCRETE ROADS [CHAP. VU 

prevent it from becoming slippery, but this is unnecessary; and the 
making of grooves in the surface is very objectionable even on grades, 
since the grooves weaken the slab and greatly increase the wear. 

Several devices have been invented to facilitate the finishing 
of the surface. One method is to draw an 8- to 12-inch rubber belt 
or a rubber-faced canvas belt, or a plain canvas belt back and forth 
across the pavement after it has been struck off with the template, 
and to move it along the pavement as the surface is finished. For 
the best results the surface should be given a second floating just as 
the cement takes its initial set. When armored contraction joints 
(§465) are used, it is necessary to do a small amount of hand floating 
near the joint. The belt finish gives a good surface at small cost.* 

The most recent method of finishing the surface is to roll it. 
The rolHng may be done in either of two ways: 1. With a roller 
about 8 inches in diameter and about 6 feet long, made of light sheet 
steel and weighing about 70 lb., attached to a long pole, the operator 
standing at the side of the road and rolling the concrete back and 
forth across the road. 2. With a roller a little longer than the con- 
crete road is wide, having a roimd steel axle projecting at each end, 
the roller being operated by a man on each side of the roadway by 
means of a suitable handle with a hole in its lower end through which 
the axle passes. Although first used in 1917, the method of finishing 
by rolling seems to secure greater strength and density than hand 
floating; and is rapidly being adopted. 

Another method is to draw a rubber garden hose in the form of the 
letter U along the pavement. Still another method is to draw a 
1-inch plank endwise back and forth over the concrete by means of a 
rope attached to each end. A long-handled float has been used, but 
opinions differ as to its efficiency. 

464. Curing and Protecting. The green concrete may be seriously 
damaged by the too rapid drying out of the surface in hot or windy 
weather, or by exposure to low temperature, or by being opened to 
travel too soon. 

If the concrete dries out too rapidly, the surface becomes friable 
and chalky, and is covered with shrinkage cracks, which are a source 
of weakness. Therefore in hot or windy weather it is usually neces- 
sary to cover the concrete with canvas for at least half a day after 
it is floated. This canvas is made either in 6-foot strips 2 or 3 
feet longer than the pavement is wide, or in long strips a little 

* Engineering News, Vol. 77 (1917), p. 197-8; or Illinois Highways, Dec, 1916, p. 155-56. 



AKT. 2] 



THE CONSTKUCTION 



253 



wider than the pavement, mounted on rollers. In either case, if 
the concrete has not set, the canvas should be supported on frames 
so it will not touch the concrete. 




Fig. 83. — Concrete Road Covered with 

Canvas. 



Fig. 83 shows a concrete road 
protected by canvas. Notice 
that the earth at the sides of 
the concrete has been plowed 
preparatory to covering the con- 
crete with it. 

When the concrete has hard- 
ened sufficiently, the canvas is 
removed, and the pavement is 
covered with at least 2 inches of 
earth which should ordinarily be 
kept wet for 10 to 15 days. 
Shavings or straw are sometimes 
used to cover a new concrete 
pavement ; but they are liable to 

be washed into piles in sprinkling or to be blown off, in either case 
leaving exposed patches 

If there is danger from frost, the ingredients should be heated 
before the concrete is mixed (see § 451); and after being placed the 
green concrete should be protected by canvas or building paper. 
The former is the easier handled, and is usually more economical. 
In extreme cases steam may be blown imder the canvas or building 
paper. To protect the concrete after the first night, a layer of straw 
with a little earth on it has been used. 

Great care should be exercised in opening the pavement to travel. 
The length of time necessary to keep the pavement closed will depend 
entirely upon weather conditions. During warm weather the pave- 
ment should be kept closed to travel for at least fourteen days, and 
preferably for three weeks. When the conditions are such that the 
temperature of concrete is less than 50° when placed, hardening takes 
place very slowly. When a concrete pavement has been laid in the 
late fall, it is sometimes difficult to determine when it will be safe to 
open the road. In rare cases it may be necessary, owing to local 
conditions, to open the road or street before it is absolutely safe. 
Under such conditions if about 2 inches of straw is placed on the 
pavement and this is covered with a few inches of earth, the pave- 
ment will be protected sufficiently against abrasion to allow the open- 
ing of the road sooner than could be safely done without such pro- 



254 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. VII 



tection. This cover will, however, not minimize the danger of dam- 
age to the pavement by heavy loads, which will tend to crack a 
pavement that has not developed its full strength. 

465. Contraction Joints. Concrete expands and contracts 
with changes of temperature and moisture. Since the pavement is 
ordinarily laid in warm weather, the. contraction is likely to be greater 
than the expansion; and besides the concrete can resist the com- 
pression due to expansion better than the tension due to contraction. 
To prevent the formation of unsightly and irregular cracks due to 
contraction, it is customary to provide contraction joints at regular 
intervals. If the pavement has curbs, longitudinal contraction 
joints also are provided at each curb. Concrete roads and pave- 
ments are usually provided with transverse contraction joints from 
25 to 75 feet apart, usually about 50 feet. 

466. Contraction joints are made in any of three ways: (1) by 
inserting a wood strip or steel plate, and removing it after the con- 




FiG, 84. — Assembling Armored Joint. 



Crete is in place, and then pouring in an elastic mastic of tar or 
asphalt; (2) by inserting during construction a sheet of mastic pre- 
pared for the purpose; or (3) by inserting one or more thicknesses 
of tar paper or asphalt felt. 

The longitudinal contraction joints are made by placing next 
to the curb a layer of bituminous mastic from | to 1 inch thick, de- 
pending upon the width of the pavement. 

The transverse joints are sometimes protected by placing a soft- 
steel J-inch plate on each side of a J-inch sheet of mastic. The plates 
are provided with projections which securely tie or bind them to the 
concrete. Fig. 84 shows the two metal plates and the intervening 
sheet of mastic or tar paper being clamped together preparatory 



ART. 2] 



THE CONSTRUCTION 



255 



to being set into the pavement. Fig. 85 shows the joint being 
installed in position in the concrete. Notice that the plates are 
suspended from a temporary bar which rests on the side forms. 




Fig. 85. — Installing Armored Joint. 

Fig. 77, page 247, shows an armored joint ahriost covered with 
concrete; but notice that there is no temporary supporting bar as in 
Fig. 77. These protected joints are expensive, complicated to 
install, and do not wear down with the concrete; and consequently 
are falling into disrepute. 

The most popular joint filler for transverse joints is one or more 
thicknesses of 3-ply tar paper, which when new projects shghtly 
above the surface of the pavement. Fig. 86 shows the method 




Fig. 86. — Finishing Tar-Paper Joint. 



Fig. 87. — Trimming Tar-Paper Joint. 



of finishing the concrete next to one of these joints; and Fig. 87 
shows the way of trimming off the surplus tar paper. Some 
engineers use two thicknesses in hot weather, and three in cool 



256 PORTLAND-CEMENT CONCRETE ROADS [cHAP. VII 

weather. A single thickness of 3-ply tar paper has been entirely 
satisfactory. To facilitate the insertion of the tar paper, it is tied 
with a small string to a steel plate or 1-inch plank thinned a little at 
its lower edge and cut to the proper width and crown, and the plank 
and paper are set into place and concrete is deposited on both sides 
of the plank; and then the strings are cut, the plank and strings 
removed, and the space occupied by the plank is tamped full of con- 
crete. 

It is important that the face of the joint be truly vertical, or 
there is danger of one slab's sliding up and over the next one 

A transverse joint is likely to be a source of weakness owing to the 
tendency to force an excess of cement, and consequently a deficiency 
of stone, next to the joint; and also owing to the tendency of the con- 
crete to chip out next to the joint. These tendencies arc reduced 
somewhat by the use of a split float (Fig. 86), which will finish 
both sides of the joint at the same time. 

467. Sometimes the contraction joints are placed at an angle 
with the length of the road, which is an advantage if there is either 
an elevation or depression at the joint; but if the joints are properly 
made and maintained, the extra length is only a needless expense, 
and besides it is very difiicult to strike the surface adjacent to the 
diagonal joint. 

468. A number of attempts nave been made to determine mathe- 
matically the proper distance between contraction joints; but 
there is so much uncertainty in each of the several factors of the prob- 
lem that any such computation is practically worthless. There 
seems to a growing tendency to narrow the thickness of the joint 
filler and to lengthen the distance between the joints. Some rural 
roads have been built without any contraction joints, on the theory 
that when cracks form they can be filled with pitch. In filKng a 
crack the mastic is piled up over the crack a Uttle to protect the edge 
of the concrete. Of course, all contraction cracks as well as all others 
should be kept full of bituminous filler as a part of the maintenance 
of the road. 

469. Reinforcement. Some engineers claim that concrete 
pavements should be reinforced to prevent cracks due (1) to changes 
of temperature and moisture, (2) to improper drainage and defective 
foundation, (3) to insufficient thickness of concrete, and (4) to 
defective construction. The most simple and most economical 
method of eliminating each of the three last classes of cracks is to 
remove the cause. The use of reinforcement simply distributes the 



ART. 2] THE CONSTRUCTION 257 

cracks due to changes of temperature and moisture, thus substi- 
tuting many minute cracks for a few large ones. The large cracks 
can be protected by filling with tar or asphalt, while the small ones 
can not be protected, or rather will not be protected, and hence will 
be a cause of deterioration of the pavement. 

It is impossible to compute with any degree of accuracy the 
amount of reinforcement required to prevent temperature cracks, 
and much more so to determine the amount required to prevent 
cracks due to the other causes mentioned in the preceding para- 
graph. To be most efficient in preventing cracking due to some of 
the causes, the reinforcement should be near the top of the slab, and 
for others near the bottom. When reinforcement is used, it is gen- 
erally placed 2 inches from the top; but when so placed it is not 
very effective. With the same depth of embedment the reinforce- 
ment in a thin broad slab is much less effective than that in a 
narrow deep beam. Further, the reinforcement is expensive, and is 
troublesome to install. The reinforcement usually adds 15 to 20 
cents per square yard to the cost of the pavement. When reinforce- 
ment is used, the concrete must be laid in two courses, which further 
adds to the expense, and also there is danger that the two courses 
may not thoroughly unite. Those who professedly use reinforce- 
ment primarily to prevent temperature cracks, usually recommend' 
that contraction joints be constructed 75 feet apart; but many 
concrete roads have been reasonably satisfactory without either 
reinforcement or contraction joints. 

However, reinforcement does serve to keep the parts of the slab 
from separating after cracks have formed. 

It is probably unwise to reinforce a concrete pavement, except 
perhaps where the slab rests upon spongy soil which it is not prac- 
ticable to replace, or where it is impossible to obtain adequate drain- 
age. Reinforcement is more common for wide city pavements than 
for narrow country roads. Only 5 per cent of all concrete roads and 
pavements laid in this country have been reinforced. 

470. Shoulders. The shoulders should be partially con- 
structed when the subgrade is prepared; and after the concrete is 
completed and cured, the shoulder should be finished. It is usual 
to reinforce the earth shoulder by adding broken stone or coarse 
gravel, making it 4 to 6 inches thick next to the paved roadway and 
feathering out to nothing at a distance of 3 to 5 feet out. The 
shoulders should be thoroughly consolidated by rolling, and should 
be finished flush with the pavement but not any above it. 



258 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. VII 



Some competent engineers do not strengthen the earth shoulders 
of double track roads; but this seems of doubtful widsom, because 
there is always more or less turning off from the pavement, even on 
double-track roads, — if for no other reason, than that the slow-moving 
vehicle may give the right-of-way to the fast-moving one, as is 
required by law in some states. 

471. Curbs. A concrete road ordinarily does not have a curb, 
since it is expected that vehicles will turn off upon the shoulders. 
When a road is in a cut or upon a hillside, it may be necessary to 
provide a gutter for drainage. If the road surface is water-bound 
gravel or water-bound macadam, the gutter must be outside of the 



X 







Winnetka, ///. 






Geneseo, I//. 



K-4- 







Indianapo/h, Ind 



K/mber/y, H//s. 



Fig. 88. — Integral Curbs for Concrete Pavements. 



paved way, since the flowing water would destroy the road surface; 
but if the road is a concrete one, flowing water Vvdll not damage it, 
and consequently instead of building a gutter outside of the paved 
way, it is considerably cheaper to build a curb against or on the edge 
of the concrete slab, and allow the water to flow down the edge of the 
concrete slab. 

The curb is most cheaply constructed if it is cast at the same time 
as the slab, and hence is called an integral curb. The integral curb 
is usually cheaper to build than a durable gutter, and in a cut its use 
saves considerable excavation. 

The integral curb has been used for concrete driveways for a 
number of years, but was first used for pubhc roads about 1914. 

Various forms of integral curbs have been used. The simplest is 
made by shaping the end of the strike board to form a low curb, but 



ART. 2] 



THE CONSTRUCTION 



259 



Fonji 



this form is used only on park drives where a prominent curb is not 
desired but where a waterway is necessary. The cost of such curbs 
is nearly neghgible. 

Fig. 88 shows four types of integral curbs that have been used.* 
These curbs are constructed by making a form board for the edge 
of the roadway slab and the back of the curb, and forming the face of 
the curb by clamping with carpenter's screw clamps a form board 
against spacing diaphragms. The curbs shown in Fig. 88 are much 
cheaper to construct than the type of combined concrete curb and 
gutter used with other forms of pavements — see Chapter XIV. 

Fig. 89 shows the from used in integral curb construction 
in Milwaukee, Wisconsin, f As soon as the pavement is struck 
off, the form is set in 
place and weighted with 
bags of sand to prevent 
it from rising when the 
concrete is deposited in 
it. 

The concrete founda- 
tion for brick pave- 
ments for rural roads 
were formerly built with 
integral curbs similar to 
the last two shown in 
Fig. 88 except that the 
corner at both the bottom and the top of the inside face was made 
square rather than rounded. Strictly speaking the projection on the 
concrete foundation is not a curb, since it does not project above 
the pavement. It is usually referred to as an integral curb; but a 
more appropriate name is concrete edging, which is occasionally used. 
At present brick pavements for rural roads are usually built mono- 
lithic (§ 982), which does away with the need of any curb or edging. 

472. Cost of Concrete Road. The cost of a concrete road- 
slab varies with the specifications and the local conditions, and hence 
no record of cost will apply strictly in all cases; but cost data are 
useful for comparison and as a guide in preparing estimates. 

Some of the following cost data are a little out of date; but prices 
for 1917 are abnormal owing to the disturbance due to the Great 
European War, and besides any cost data presented in a book of this 

* Engineering Record, Vol. 71 (1915), p. 111. 

t Engineering and Contracting, Vol. 45 (1916), p. 544. 




Form for Integral Ctjeb. 



260 PORTLAND-CEMENT CONCRETE ROADS [chAP. VII 

character soon becomes out of date. The costs given below are full, 
and are believed to be accurate and representative. They are inter- 
esting chiefly as showing relative values in different localities, and of 
the different parts of the work. For current prices for concrete 
roads, consult the construction news in technical journals. 

473. Cost of Materials. For data on the cost of portland 
cement, see §425; for the same for sand and gravel, see §426; 
and for broken stone, see § 427. For more recent prices, see the 
market reports in current technical journals. For information con- 
cerning the amount of the several ingredients required for a cubic 
yard of concrete, see § 428-29. 

474. Cost of Labor. The work of the two following examples 
of hand and machine mixing was done under substantially the same 
conditions and hence the results are fairly comparable. Notice 
that the cost with hand mixing is about a half more than with ma- 
chine mixing. Further, it is probable that no practicable amount of 
hand mixing will give as good concrete as ordinary machine mixing; 
or in other words, if the hand mixing had been as thorough as the 
machine mixing, the difference in cost would probably have been still 
greater. Hand mixing has practically been abandoned in concrete 
road and pavement work. 

475. Hand Mixing. The construction was two-course work — ^a 
5-inch 1:3:5 base and a 2-inch 1 : 2 wearing coat; but the cost is 
not given separately for the base and the top. There were steel- 
protected contraction joints every 25 feet. The pavement was 30 
feet wide.* 

Organization. Cost. 

Cts. per 8q. yd. 

1 foreman @ 40^ per hour 2 . 10 

1 finisher @ 40^ 

1 finisher's helper @ 20ff 

Total for finishing 2.88 

1 form setter @ 25«f 

1 form setter's helper (5) 20ff 

Total for setting forms , 1 . 76 

8 mixers @, 20?zf 

1 cement man @ 20^ 

1 man on sand @ 20^ 

4 men on broken stone @ 20jif 

2 spreaders @ 20^ 

Total for mixing and spreading 12 . 24 

1 watchman . 50 

Total for mixing and laying 19 . 48 

* Engineering and Contracting, Vol. 38 (1912), p. 710. 



ART. 2] THE CONSTRUCTION 261 

476. Machine Mixing. The width of pavement was 30 feet. 
The construction was two-course work, — a 5-inch 1:3:5 base and 
a IJ-inch 1:1:1 wearing coat.* 

Organization. Cost. 

Cts. per sq. yd. 

Base: 

9 men on broken stoiie @ 22|^ 2 . 18 

3 men on sand @ 22^,zi 0.73 

1 man at skip @ 22|^ 0.24 

1 man wheeling cement @ 22^^ . 24 

1 man leveling concrete @ 25^ . 27 

1 helper leveling concrete @ 22^j!5 . 24 

1 tamper @ 22U 0.24 

1 engineer @ 25^ 0.27 

1 fireman @ 25^ 0.27 

1 bucket operator @ 15^ . 16 

1 water boy @ 5^ . 05 

1 sack boy @5^. ., 0.05 

1 . foreman @ 45^ . 48 

Total for base 5.43 

Wearing Coat: 

4 men on granite chips @ 221^:5 . 48 

4 men on sand @ 22|ff 0.48 

2 men at skip @ 22^^ 0.24 

2 men wheeling cement @ 22^^ . 24 

2 rough spreaders @ 22|^ . 24 

1 fine spreader and tamper @ 25^ . 13 

1 fireman @ 25^ 0. 13 

1 engine runner @ 25^ .13 

1 bucket operator @ 15^ . 08 

1 sack boy @ 5^ 0.02 

1 water boy @ 5^ . 02 

1 foreman @ 45)i5 . 24 

1 finisher @ 25)/^ 0. 61 

1 finisher's helper @ 22^f^ ' 0.55 

Total for wearing coat 3 . 61 

Setting Forms: 

1 man @ 22||^ 0.42 

Miscellaneous: 

1 man trimming grade @ 22|^ . 43 

2 men cleaning up sand and stone . 36 

moving machine 1 . 30 

Total for miscellaneous labor 2 . 09 

Grand total 13 . 50 

* Engineering and Contracting Vol. 38 (1912), p. 710.. 



262 



PORTLAND-CEMENT CONCRETE ROADS [cHAP. VII 



477. Relative Cost of Labor and Materials. The following data 
are the averages for seven Michigan State-aid roads, eight Wayne 
Co. (Mich.) roads, and all the concrete roads built by the IlHnois 
Highway Commission in 1912-13. 

Materials : aggregates 27 . 7 per cent 

cement 21.6 " 

expansion joints and supplies 6.4 " 



Total materials 55 . 7 

Labor 44 . 3 



Total 100.0 

478. Total Cost. The three examples in Table 29 are believed 
to be fairly representative. 

The values given in Table 30, page 263, are the average of the 
contractor's costs exclusive of over-head expenses and profits, but 
inclusive of the preliminary shaping of the surface and the finishing 
of the earth shoulders; and include representative states. 

For more recent data, see the bidding prices in the construction 
news of current technical journals. 

TABLE 29 
Cost of One-Course Concrete Slab for Roads in Illinois * 

DATA AND DIIMENSIONS 



Items. 


McLean. 


CAEI,i:v-Yir.LE. 


Springfield. 




5 000 

6 

45 

0.12 

$1.06 

0.29 

SI. 25 
0.22 
0.50 


7 111 
6.5 
16 
1.5 
0.98 
0.33 

$1.25 
0.225 
0.50 


5 594 


Thickness of pavement, inches 

Width of pavement, feet 

Length of haul, miles 

Cost of cement per bbl 


7 
18 
.12 
1 025 


Barrels of cement used per sq. yd 

Cost of gravel per cu. yd. f.o.b. desti- 
nation 

Labor, price per hour 

Teams, piice per hour 


0.29 

$1.25 
0.25 
0.50 



COST OF LABOR AND SUPPLIES 



Items. 



Superintendence 

Shaping subgrade 

Loading and hauling- sand and stone. 

Mixing and placing concrete 

Watchman and miscellaneous labor. . 

Cost of sand and stone 

Cost of cement 

Expansion joints 

Coal, oil, and miscellaneous supplies. 

Forms and other lumber 

Filling curb expansion joints 

Reinforcing .steel 

Excavation 

Trimming shoulders 



Totals. 



140.00 

307.11 

267.34 

414.63 

110.26 

017.63 

547.15 

48.67 

30.75 

35.00 

45.18 



Per 

Sq.yd. 



$0 



028 
061 
053 
083 
022 
204 
309 
010 
006 
007 
010 



Total $3 964.02 $0,793 $5 803.07 $0.8176 $5 794.76 $1.0352 



TOT.\LS. 



157.50 
108.70 
795.05 
700.58 
131.46 
741.00 
307.90 
112.40 
25.00 
31.75 



100.00 
591.73 



Per 

Sq. yd. 



$0 . 0220 
.0153 
.1120 
.0986 
.0184 
.1050 
.3246 
.0156 
. 0034 
.0047 



.0140 
.0840 



Totals. 



5 202.00 

343.44 

603.50 

644.25 

383.75 

1 622.01 

1551.17 

206.74 

119.19 

18.33 



211.38 



* Report 111. Highway Com., 1912, p. 240, 241, and 247, respectively 



Per 

Sq. yd. 



.0361 
.0415 
.1078 
.1150 
.0686 
.2897 
.2772 
.0369 
.0213 
.0033 



, 0378 



ART. 2] THE CONSTRUCTION 263 

TABLE 30 

Average Cost per Square Yard of Concrete Road Slabs in 1915 * 

Connecticut $1 . 13 Missouri $1 .09 

Illinois 1 .03 New Jersey 1 .23 

Indiana 0.98 New York 0.98 

Iowa 1.19 Ohio 1.02 

Kansas 1 . 28 Pennsylvania 1 .01 

Maryland 1 .08 Texas 1 . 15 

Massachusetts . 95 West Virginia 1 . 03 

Michigan 1 . 10 Wisconsin 1 .02 

Minnesota 1.11 

479. CHARACTERISTICS OF A CONCRETE ROAD. The character- 
istics of a well-built concrete road are: 1. It is reasonable in first 
cost in proportion to its probable durability. 2. It has a low tractive 
resistance, but gives a good foothold for horses and automobiles. 3. 
It is free from dust. 4. It is easily maintained. 5. It is reasonably 
durable when properly maintained. 6. Its only fault is that the 
color is somewhat trying to the eyes of the user; although the light 
color is some advantage at night. 

480. Concrete Street Pavements. The preceding discussion 
has reference primarily to strips of concrete 10 to 20 feet wide for 
rural roads, since concrete is in more common use for rural roads 
than for city streets. The same methods without material change 
can be employed for pavements up to 30 feet wide; but for wider 
pavements it is necessary to modify the plan in one of two ways as 
follows: (1) Make a longitudinal joint in the middle of the street 
and lay half of the street at a time; or (2) insert screeds transversely 
to the street, and strike the concrete with a straight edge held parallel 
to the curb. 

On a wide street the finishing is done with a belt or a board laid 
flatwise and reaching half-way across the pavement, the end at 
the curb being handled by a man and the end at the center being 
guided by a small rope in the hands of a man standing on the remote 
curb. The former method is considered the better, since a longi- 
tudinal joint is undesirable. Such joints are sometimes protected 
with steel plates, and should always be covered with tar; but even 
then a rut is likely to form along them. 

Concrete pavements having separate curbs require longitudinal 
contraction joints at each edge (§ 465-68); but the integral curb 
(§ 471) eliminates this complication. 

* Data collected by the Portland Cement Association. 



264 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. VII 



481. Specifications. Complete specifications for concrete 
roads are printed by the several State Highway Departments, of 
which copies may doubtless be had by citizens of the respective 
states upon request. The Portland Cement Association publishes for 
gratuitous distribution the specifications adopted by the American 
Concrete Institute and recommended by the 1916 National Con- 
ference on Concrete Road Building, copies of which may be had 
gratuiously of the Secretary, Portland Cement Association, 111 W. 
Washington St., Chicago. 



Art. 3. Maintenance 

482. Character of work Required. The work required to 
maintain the concrete slab is: (1) keep the joints and cracks filled 
with bituminous cement; (2) fill with bituminous cement any small 
pits that appear; (3) clean out any holes left where pebbles have 




I^G. 90. — IPimatQ A Diagonal Crack. 



been dislodged or where a friable fragment has disintegrated, and fill 
them with bituminous concrete; and (4) repair any places where the 
concrete is otherwise defective. 

The bituminous material may be either a heavy grade of refined 
tar or a corresponding grade of asphalt. After the bituminous 



ART. 3] MAINTENANCE 265 

material has been applied, its surface should be sprinkled with coarse 
sand or fine chips of a hard stone. 

Fig. 90 shows the method of repairing a transverse contraction 
joint. 

Before being filled, all cracks and joints should be swept clean 
with rattan or steel brooms. The old tar need not be removed ; but 
any matted earth or other foreign material not removed by the first 
sweeping should be loosened and removed with a steel hook. It is 
usually necessary to cover all joints and fill all cracks twice each year. 

The pits and the cup-like holes from which pebbles, sticks, etc., 
have been dislodged, unless early filled, will enlarge rapidly under 
travel. Where defects of any considerable size are to be repaired, 
the edges should be made vertical with a chisel and the depth of the 
hole increased to 1 inch, if it is not already that deep. The hole 
should be thoroughly cleaned and painted with hot tar; and then be 
filled with bituminous concrete and sprinkled with coarse sand or fine 
hard stone chips. 

When it is necessary to repair any considerable defective portion 
of the concrete, the place to be patched should be trimmed and 
cleaned as described above, and painted with neat cement mortar; 
and then the hole should be tamped solidly full of good portland- 
cement concrete. The patch should be kept damp and protected 
from travel until the cement has fully set. 

483. The above method of maintenance will probably serve 
indefinitely, and will preserve the surface except for the natural 
wearing away of the concrete by travel. 

484. Bituminous Surface. Many attempts have been made 
to cover the surface of a concrete road with a bituminous coating. 
This phase of the subject is considered in Art. 2 of Chapter VIII. 

485. Cost of Maintenance. The cost of maintenance con- 
sists of the annual expense for repairs and the annual contribution to 
a fund for rebuilding the slab when it is worn out. The introduction 
of concrete roads is so recent, particularly in proportion to their life, 
that no reliable data have been accumulated as to the second item 
of the cost of maintenance. There are reasonably accurate data for 
the annual cost of repairs, but as a rule there is no information as to 
amount of or character of the travel on the road; and therefore it is 
not possible to make any accurate comparisons between such data. 
Further, no standard has been established as to what constitutes 
good maintenance; and no system of doing the work has been 
fully tested. 



266 



PORTLAND-CEMENT CONCRETE ROADS 



[chap. 



VII 



Apparently the most complete data are those obtained in 1915 
by the Illinois Highway Department.* The average annual cost for 
repairs on 75 miles of concrete rural roads in comparatively short 
sections, was 0.4 cent* per square yard for supervision, labor, equip- 
ment and materials. Most of the roads were built in 1914 or 1915. 
Two methods of maintenance were tried, — (1) by the use of a one- 
horse wagon drawing a portable heating-kettle, and (2) by an auto- 
mobile truck carrying a heating tank. By the first method the total 
cost was 0.32 cent per square yard per treatment, and by the second 
0.22 cent. In this work it was found that joints, even though pro- 
tected by steel plates, required about the same attention as ordinary 
cracks. 

In Connecticut the average cost of repairs to the concrete slab 
was 0.4 cent per square yard per annum and to drainage 0.3 cent 
per square yard, or a total of 0.7 cent. 



* Illinois Highways, August, 1915, p. 118-22; or Engineering and Contracting, Vol. 47 (1917) 
p. 14. 



CHAPTER VIII 
BITUMINOUS ROAD MATERIALS 

486. Definitions. Bitumen. A mixture of native or pyro- 
genous hydrocarbons and their non-metalHc derivatives. It may be 
a gas, hquid, or soHd; and if sohd, is soluble in carbon disulphide. 

487. Bituminous Material. Any material containing bitumen 
or constituting a source of bitumen. Bituminous coal, peat, etc., 
are caUed pyro-bitumens because a bitumen may be produced from 
them by distillation. The ordinary bituminous materials used in 
roads and pavements are asphalt, petroleum, and tar.* 

488. Cut-back Product. A petroleum or tar residuum which 
has been fluxed with distillate. 

489. Flux. Fluid oil or tar which is incorporated with asphalt, 
petroleum, or tar residuum for the purpose of reducing their con- 
sistency. 

Art. 1. Asphalt 

490. Definitions. Asphalt. Sohd or semi-soHd native bitumen 
or solid or semi-solid bitumen obtained by refining petroleum, which 
consists of a mixture of hydrocarbons and which melts upon the 
application of heat. Asphalt is usually found associated with 
various mineral and organic substances. Different varieties of 
asphalt are called albertite, grahamite, gilsonite, turrellite. uintatite, 
wurtzelite, etc. 

491. Crude Asphalt. A native mixture of bitumen, sand, clay, 
water, organic matter, etc. 

492. Refined Asphalt. A native mixture after it has been freed 
wholly or in part from water and organic and inorganic matter by 
being heated. 

* For detailed explanations of the methods employed in testing bituminous road materials, 
see Bulletin 314 of the Office of Public Roads and Rural Engineering, U. S. Department 
of Agriculture, Washington, D. C, 1915. 

267 



268 BITUMINOUS ROAD MATERIALS [CHAP. VIII 

493. Rock Asphalt. A limestone or sandstone naturally impreg- 
nated with asphalt. Rock asphalt is the principal form of asphalt 
used in Europe for paving purposes, and there is usually designated 
as asphalt. 

494. Asphaltic Cement. Refined asphalt which has been mixed 
with some solvent to increase its plasticity, adhesiveness, and tenacity. 

495. CHARACTERISTICS OF Asphalt. As usually found asphalt is 
of a dark brown or ghstening black color. It varies in hardness from 
a viscous Hquid to about 3| on the Dana scale. When rubbed or 
freshly broken, it emits a pecuUar bituminous odor, and has a sUght 
sour smell. Its specific gravity in the natural state varies from 0.96 
to 1.68 according to its porosity and the amount and the character 
of the impurities present. It is insoluble in water; but is more or 
less soluble in carbon disulphide, alcohol, turpentine, ether, naphtha, 
and petroleum. 

Asphalt has an appearance somewhat like coal tar. The prin- 
cipal method of distinguishing asphalt from coal tar, available 
to the lajmian, is the odor. The tar emits a sharp, acrid odor; 
while both the crude and the refined asphalt when cold give a weak 
clay-Hke odor, and must be rubbed to obtain the distinctive bitumi- 
nous odor. If tar is mixed with asphalt, the presence of 25 per cent 
will be revealed by the odor. When being laid in a road or pave- 
ment, tar gives off a bluish vapor, while asphalt emits a white vapor. 

496. Asphaltic hmestone, when freshly broken, varies in color 
from chocolate brown to black, the color being darker as the pro- 
portion of asphalt is greater. The percentage of asphalt permeating 
the hmestone varies in different deposits and in different parts of the 
same mine, usually ranging from 1 to 20 per cent. 

Asphaltic sandstone contains from 1 to 70 per cent of asphalt. 
The grain is sometimes dense and sometimes porous, sometimes very 
fine and sometimes coarse. 

497. Sources of Asphalt. Liquid asphalt, or maltha as it is 
usually called, is found in large quantities in California; but soHd or 
natural asphalt is not found to any great extent in the United 
States. The principal kinds of the natural asphalts used in this 
country are: Trinidad, Bermudez, and California. 

498. Trinidad Asphalt. The Island of Trinidad, near the north- 
east coast of Venezuela, South America, supplied something like 
90 per cent of all the asphalt used in the world from about 1875 to 
1900; and at present the Island of Trinidad is the main source of 
supply of the native asphalt used in the United States. In south- 



ART. 1] ASPHALT 269 

west corner of the Island is the so-called pitch-lake, which has an 
area of about 115 acres. The surface of the lake has an elevation 
of 138 feet above the sea-level, and near the center the asphalt has a 
depth of 78 feet. As a rule the surface of the asphalt is sufficiently 
hard that teams may be driven over it; but the whole mass is in 
constant motion around several vortices, as shown by trunks of 
trees which rise and after a time again disappear. Excavations 
made during the day close up during the night. 

The asphalt is excavated with picks and shovels, conveyed to 
the shore in carts, and Hghtered to vessels off-shore. On the sea 
voyage it becomes compacted into a sohd mass and must be again 
broken up with picks. The crude asphalt is mixed with much 
earthy and a little vegetable matter and water, and is dark brown. 

The crude material is refined by placing it in kettles or open 
tanks and heating it for three or four days, during which time the 
water is evaporated, the vegetable matter rises to the surface and 
is skimmed off, and the earthy material settles to the bottom. Great 
care is required in the refining process not to heat the apshalt to a 
point where chemical changes take place. The refined asphalt 
must be softened by the addition of some fluxing material before it 
is ready for use in the pavement. 

499. Bermudez Asphalt. A lake in the State of Bermudez, 
Venezuela, South America, supplies large quantities of asphalt. 
The crude asphalt consists of bitumen mixed with sand, clay, and 
vegetable matter; and is refined in the same way as Trinidad asphalt, 
but more rapidly, since it contains less water and mineral matter. 

500. California Asphalt. Cahfornia is the principal producer of 
asphalt in the United States; and is said to have not only larger 
quantities of asphalt than any other equal area in the world, but a 
greater variety of forms — sohd and hquid asphalt, and asphaltic 
Hmestones and sandstones — and in more locahties. Maltha ('' liquid 
asphalt ") is found chiefly at Carpinteria, Santa Barbara County, 
near the sea shore; and sohd asphalt is found at La Patera, Santa 
Barbara County, also near the sea shore. Asphaltic limestone and 
sandstone are found at a number of places in California, in all degrees 
of richness and consistency. The principal deposits are at Santa 
Cruz, San Luis Obispo, and Kings City. The asphalt is extracted 
from the stone by heating the mass in a tank and drawing off the 
liquid asphalt. 

501. The base of the CaHfornia petroleums is asphaltic, as dis- 
tinguished from the paraffin base of the eastern oils; and the process 



270 



BITUMINOUS ROAD MATERIALS 



[chap, vm 



of refining petroleum leaves the asphalt or maltha as a residue, and 
at several places asphalt is produced in this way from crude petro- 
leum. 

502. Petroleiun Residue. Some crude petroleums on distilla- 
tion have an asphalt residue (see § 547). Three fourths of all the 
asphalt used in the United States is obtained from asphaltic petro- 
leums. Such material is usually called oil asphalt. 

503. Other American Asphalts. Considerable asphalt is shipped 
to the United States from mines at Inciarte and La Paz, State of 
ZuHa, Venezuela, South America. It is usually called Maracaibo 
asphalt from the gulf and lake of that name near the mines. 

Asphalt is found in much smaller quantities, but sufficient to 
be of considerable commercial importance, in Utah, Colorado, 
Indian Territory, Texas, and Kentucky. One of the most important 
of these is Gilsonite, a solid and nearly pure native bitumen found in 
Utah and Colorado. 

Several deposits of natural asphalt exist in Cuba and along the 
Gulf Coast of Mexico. 

504. Shipping Asphalt. Refined asphalt is shipped in barrels 

or metal drums or in tank cars. 




Fig. 91. — Unloading Asphalt Binder. 



Notice 



Fig. 91 shows the method of 
unloading asphalt binder from 
the tank car to the machine 
which distributes it upon the 
asphalt-bound macadam road. 
In the left foreground is the 
motor - truck distributor, and 
behind it is a portable heater 
that the tank is covered with 



for heating the asphalt, 
blankets. 

505. Desirable Properties of Asphalt. The character- 
istics required in an asphalt differ according to the purpose for 
which it is to be used; but in general any asphalt for use in roads 
or pavements should have the following properties: 1, chemical 
stability; 2, freedom from decomposition products; 3, binding 
power; 4, resiliency, and 5, waterproof ness. 

Apparently it is impossible to devise any tests to measure directly 
some of these properties; and the difficulties of devising a series 
of tests is increased by the variation in the character of the different 
materials. 

506. Chemical Stability. The chemical stability of a bituminous 



AKT. 1] ASPHALT 271 

«ement is indicated somewhat by the extent to which the material 
is volatihzed under standard temperature conditions. The harden- 
ing of the bituminous cement due to evaporation and oxidation is 
determined by making penetration tests before and after volatiUza- 
tion. The temperature at which the material gives off vapor enough 
to ignite gives further indication of chemical stability. 

507. Freedom from Decomposition Products. If the refining 
process has been carried on at a too high temperature, the cement 
may have been partially decomposed. This condition is indicated 
by the amount of free carbon and other decomposition products that 
are separated by certain solvents. If the material is a fluxed nat- 
ural asphalt, these tests throw some light upon the character of the 
flux. 

508. Binding Power. It is important that the bituminous 
material shall have cementing or binding power, particularly at 
summer temperatures. There is no single test for this property. 
The ductility test gives some indication concerning cementing value. 

509. Resiliency. It is important that the bituminous cement 
shall have the power to absorb shock and thus prevent the blow 
of the wheel or the hoof from destroying the road or pavement sur- 
face. This requires that the cement shall have resiliency and mal- 
leability, which depend somewhat upon consistency. 

510. Waterproofness. The bituminous material should be water- 
proof so as to prevent water from penetrating the body of the road 
and doing damage by freezing or softening the subgrade. 

511. TESTS OF Bituminous Materials. Below are the tests 
usually applied to bituminous materials, and a brief statement 
of the significance of each. All of these tests (§ 512-27) are apphed 
to asphalts, but only the first eight (§ 512-19) are apphed to oils and 
tars.* 

512. Foam Test. This test is applied to asphalts and tars to 
determine the presence of water. Water is chiefly objectionable 
since it makes the material difficult to handle when heated above the 
boihng point of water, because the steam makes the oil or tar foam 
or froth. 

513. Specific Gravity. This test is valuable mainly as a means of 



♦ For a detailed account of the method of making the tests and also illustrations of the 
apparatus used, see Bulletin 314 of the U. S. Department of Agriculture, December 10, 1915, 
or Hubbard's Laboratory Manual of Bituminous Materials, 8vo, p. 159, John Wiley & Sons, 
New York, 1916; and for a description of the tests see Proc, Amer. Soc. of Civil Engineers, 
December, 1914, p. 3036-50. 



272 



BITUMINOUS ROAD MATERIALS 



[chap. VIII 



identifying the material; but in connection with* other tests it is 
sometimes serviceable in determining the suitability of a material 
for road purposes. The specific gravity of crude asphalt varies from 
1.04 to 1.40, and asphaltic cement from 0.96 to 1.06. The specific 
gravity of crude petroleum varies from 0.73 to 0.98, the paraffin oils 
being the lowest and the asphaltic the highest. The specific gravity 
of crude tar variesfrom 1.00 to 1.22, the water-gas tars ranging from 
1.00 to 1.10, and the coal tars from 1.10 to 1.22. The specific gravity 
of tar depends chiefly upon the amount of free carbon it contains, 
the higher the specific gravity the greater the percentage of free 
carbon. Refined tar has a higher specific gravity than crude tar, 
partly because the light hydrocarbons and the water have been 
driven off. 

514. Flash Point. The flash point is determined by either the 
open-cup or the closed-cup method, the latter being the more accu- 
rate. This test is mainly valuable as a quick means of differentiating 
between heavy crude oils and cut-back products ; but it also indicates 
the temperature at which a refined oil has been distilled. Crude 
paraffin oils usually flash lower than crude asphaltic oils. 

515. Consistency. The consistency of a bituminous material 
is an important factor, since it determines the grade of material 
suitable for a particular use, and since this test is a means of securing 
uniformity in the product. 

There are three methods or instruments in common use for deter- 
mining consistency, viz.: the Engler viscosimeter, the New York 
Testing Laboratory float apparatus, and the penetrometer. 

516. Viscosity. The viscosimeter determines the viscosity ,^i. e., 
time required for a specified amount of the material to flow through a 
standard aperture. This test is generally used for liquid bituminous 
materials. 

517. Float Apparatus. This apparatus determines the time for 
a specified quantity of semi-sohd or solid material to flow through 
an aperture; and is generally used for semi-soHd and soUd tars and 
pitches. 

518. Penetration. The penetrometer determines the distance 
a needle will penetrate the material in a specified time. Of course, 
the size of the needle, the weight on the needle, and the temperature 
of the material are carefully standardized. The penetration is usually 
stated in tenths of millimeters; but sometimes in degrees, since the 
index finger sweeps over an arc of a circle graduated to degrees. 
This apparatus is generally employed for asphalts; but it is not used 



ART. 1] ASPHALT 273 

for tars, because *the surface tension and the presence of free carbon 
considerably affect the results without materially affecting the con- 
sistency. 

519. Melting Point. The determination of the melting point is 
mainly of value as a means of identification. It is virtually a test 
of consistency (§515). As a rule as the melting point of a bituminous 
material rises, it becomes harder and more brittle. One of the char- 
acteristics of asphalt which pecuharly fits it for use in roads and 
pavements is that it has a high melting point without being brittle. 
Paraffin also has a high melting point, but it is brittle. 

520. Loss by Evaporation. This test determines the amount of 
volitilization under standard conditions. The residue is usually 
tested for penetration, melting point, and ductility. The compari- 
son of the results of these tests before and after the evaporation test 
determines the amount of hardening, which is an indication of the 
stability of the cement. 

521. Distillation. The distillation is carried on at considerable 
lower temperatures than the evaporation test, and is usually applied 
only to tars. The melting point of the residue is determined, 
and also its consistency at several temperatures. This is an impor- 
tant test of tars to determine their road-building qualities and also 
their method of preparation. 

522. Bitumen Soluble in Bisulphide. It is usually assimied that 
all matter soluble in cold carbon disulphide is bitimien. Fluid oils 
are almost wholly soluble in this material. The amount and char- 
acter of the insoluble matter are of most interest in this test. The 
insoluble matter is usually free carbon, which is of no value in road 
work. The failure to pass this test is an indication that the material 
has been overheated, i. e., '' cracked." 

523. Bitumen Soluble in Naphtha. This test is chiefly valuable 
in determining the amount of body-forming hydrocarbons in oil and 
oil products. '' No oil having less than 4 per cent insoluble in naph- 
tha will be of service in road work except as a dust preventive." 
Bitumens insoluble in naphtha are commonly called asphaltenes, 
while those soluble are called malthenes. 

524. Bitumen Soluble in Tetrachloride. The test is made for 
purposes of identification and also to determine whether the material 
has been over-heated in the process of manufacture. The bitumen 
insoluble in carbon tetrachloride but soluble in carbon disulphide is 
commonly called carbenes. 

525. Fixed Carbon. The amount of fixed carbon shows much 



274 BITUMINOUS ROAD MATERIALS [CHAP. VIII 

the same results as the bitumen insoluble in naphtha. The amount 
of fixed carbon present is an indication of the mechanical stability of 
a road oil. Paraffin oils have only little fixed carbon, while asphaltic 
oils have more, and asphalts still more. This test can not be applied 
to tar, owing to the error introduced by the presence in it of consid- 
erable free carbon. 

526. Ductility. This test consists in forming a briquette of the 
material and observing the amount of elongation before rupture. 
It is the only test for determining the cementing value of an asphalt, 
and hence is very important. 

527. Paraffin Scale. This test consists in determining the amount 
of paraffin present. It is made as a means of identification, and is 
not a very accurate test; and there is considerable difference of 
opinion as to its value. 

528. The Flux. A flux is a heavy oil or the residue from the 
distillation of petroleum which is mixed with refined asphalt to make 
it of suitable consistency for use in a sheet asphalt pavement or as 
a binder for asphaltic macadam or concrete. Fluxes are usually 
obtained from paraffin, semi-asphaltic, or asphaltic oils; and vary 
greatly in character with the petroleum from which they are derived. 
The lower the specific gravity of the flux, the less the amount required 
to produce an asphalt cement of the desired consistency. Different 
asphalts require quite different amounts of flux. For example, Ber- 
mudez asphalt requires only 7 per cent of a light flux, while Trinidad 
asphalt requires 20 per cent. 

529. Specifications for Flux. The following are the specifications 
of the American Society of Municipal Improvements, adopted 
October 14, 1915, for the flux to be used in preparing asphalt for 
sheet asphalt pavements. 

1. The flux must have a penetration greater than 350 with a No. 2 needle 
at 77° F. under a 50-gram weight appHed for one second. 

2. It shall have a specific gravity at 77° F. between 0.92 and 1.02. 

3. When 20 grams of the flux are heated for 5 hours at 325° F. in a tin 
box 2 J inches in diameter and three quarters of an inch deep after the manner 
officially prescribed, the loss shall not exceed 5 per cent by weight; and the 
residue left after such heating shall flow at 77° F. 

4. The flux shafl not flash below 350° F. when tested in a closed oU tester. 

5. It shall be soluble in carbon tetrachloride to the extent of not less 
than 99 per cent. 

530. Asphalt Cement. Asphalt cement is produced by 
mixing reflned asphalt and a flux. The asphalt should be heated to 



ART. 1] ASPHALT 275 



325 to 350° F. and the flux to 150 to 200° F. before they are mixed. 
The mixing is done by blowing air or steam, preferably the latter, 
through perforated pipes in the bottom of the melting tank. The 
mixing should be very thorough, and usually requires three or more 
hours. Care should be taken that the cement is not^ burned, par- 
ticularly if the tank is heated over a fire. The cement will harden 
if kept heated for a long time or if the agitation is kept up unduly 
long; but the cement can be softened again by adding more flux 
and mixing further. 

531. Specifications for Asphalt Cement. Asphalt cement 

is used for a bituminous surface on water-bound gravel or macadam 
roads (§ 589) and for binder in bituminous macadam and bituminous- 
concrete roads (§611 and 622); but principally for sheet asphalt 
pavements (Art. 1 of Chap. XVI), asphaltic concrete (Art. 2 of Chap. 
XVI), and also for joint filler for brick, stone-block, and wood- 
block pavements (Chap. XVI, XVII, and XIX, respectively). 

Usually separate specifications are drawn for each of the above 
uses. 

532. Whatever the purpose for which the asphalt is to be used, 
there are two classes of specifications for it, one known as general 
or open or blanket specifications, and the other as restricted or 
special or alternate specifications. The former are drawn so as 
to include all kinds of asphalt whatever their source or origin; 
and the latter consist of special requirements for each type or 
asphalt. 

Tables 31, 32 and 33, page 278, 280, and 281, show a summary 
of restricted specifications of asphalt for different uses; and § 543 
contains an example of general specifications for asphalt for sheet 
asphalt pavements. 

There is a sharp difference of opinion as to the relative merits of 
the two classes of specifications. Those who favor restricted speci- 
fications claim that there is so much difference between the different 
kinds of asphalt that it is impossible to make general requirements 
which will apply to all and at the same time define any quality so as 
to make it a real test for any particular kind of asphalt. For exam- 
ple, assume that it is desired to permit the use of any of the fom* 
asphalts of Table 31, page 278, and that it is stated that the specific 
gravity shall be from 0.96 to 1.06. The lower limit is too small to 
fix this quality in some of the asphalts, and the upper limit is too 
great to fix it for others. Again, if the specifications state that the 
penetration shall be between 90 and 160, they will permit the use 



276 BITUMINOUS ROAD MATERIALS [cHAP. VIII 

of any of the four asphalts of Table 31; but the limits are too wide 
to secure uniformity in any of the cements, and an entirely unsuitable 
material could be supplied under such specifications. 

On the other hand, equally competent asphalt specialists strongly 
dissent from the above statements; and claim that the different 
asphalts on the market are so nearly alike in their essential qualities 
as not to justify separate specifications. They claim that there is 
no more reason for separate specifications for the different asphalts 
than for separate specifications for different brands of portland 
cement. They claim that the bitimien in all asphalts is practically 
the same, and that the seeming difference in asphalts is due to the 
mineral matter which they contain. For example, Trinidad refined 
asphalt (§ 498), one of the best-known and most extensively used 
of the natural asphalts, contains about 36 per cent of mineral matter; 
and consequently its specific gravity is greater and its penetration 
is less than a more piu-e asphalt. The finely divided mineral matter 
in this asphalt does not injure it for some uses, for example, sheet 
asphalt pavements, since in practice a considerable amount of 
fine mineral matter is added to the asphalt to give it physical stability 
(§ 826). Those who advocate general specifications claim that the 
illustration concerning specific gravity in the preceding paragraph is 
wide of the mark, since a test for specific gravity is valuable only 
as a means of identifying the material, and in no way aids in deter- 
mining any essential quality. They also claim that the penetration 
of the pure bitumen in all asphalts is substantially the same; and 
that the difference in the limits is only to provide for the difference 
between heavy and fight traffic, a difference in the fineness of the 
sand, and differences in climatic conditions. 

The divergence of opinion as to the merits of the two types of 
specifications is shown by the fact that the standard specifications 
of the American Society of Municipal Improvements for bituminous 
macadam (§ 537-38), bituminous concrete (§ 539-40), and seal coat, 
(§ 541), adopt the restricted or special form of specifications for the 
asphalt; while the standard specifications of the same Society for 
asphalt concrete and sheet asphalt pavements (§ 542-43) are based 
upon general or blanket specifications for the asphalt. However, a 
recent vote shows that the weight of the society is in favor of the 
general specifications. 

533. The writing of specifications for asphaltic cement requires 
thorough laboratory knowledge of the chemical and physical char- 
acteristics of asphalt, and also practical experience in the use of the 



ART. 1] ASPHALT 277 

material.* Great care must be used in changing the limits in speci- 
fications, since a change in the value for one element may require a 
corresponding change in some other factor. Below are specifica- 
tions for asphaltic cement that have been successfully used for roads 
and pavements. 

534. Asphalt for Bituminous Surface on Water-bound Macadam. 
The following are the specifications of the Barber Asphalt Company 
for liquid asphalt for both cold and hot-surface application to 
water-bound macadam : f 

535. Liquid Asphalt A. (For Cold Application.) 1. Specific Gravity: The 
specific gravity at 60° F. shall not be less than 0.91. 

2. Flash Point: The flash point by the Tagliabue open cup shall not be less 
than 100° F. 

3. Viscosity: The specific viscosity by the Engler apparatus at 77° F., for 
the first 50 c.c. shall be between 90 and 100. 

4. Bitumen Soluble in Bisulphide: The bitumen soluble in carbon disulphide 
shall not be less than 99 per cent. 

5. Paraffin Scale: The paraffin scale determined by the Holde method shall 
not be more than 0.25 per cent. 

6. Distillation : When evaporated to 80 per cent by weight, by heating in an 
open dish at 150° F., the residue shall have at 77° F. with a No. 2 needle under a 
weight of 50 grams in 1 second, a penetration of not less than 20 mm. ; and its 
adhesiveness by the Osborne test shall not be less than 200 seconds. 

536. Liquid Asphalt B. (For Hot Application.) 1. Specific Gravity: The 
specific gravity at 60° F. shall be not less than 1.00. 

2. Flash Point. The flash point by the Cleveland cup shall be not less than 
325° F. 

3. Viscosity: The specific viscosity by the Engler apparatus at 212° F., for 
the first 50 c.c. shall be from 23 to 33. 

4. Bitumen Soluble in Disulphide: The bitumen soluble in carbon disulphide 
shall be not less than 99.0 per cent. 

5. Paraffin Scale: The paraffin scale by the Holde method shall not be 
more than 0.25 per cent. 

6. Distillation: The loss at 325° F. after 5 hours of 50 grams in a 2j by 1|- 
inch dish shall not be more than 1.0 per cent. 

7. Residue, loss by evaporation: The residue of a 5.0 mm. penetration at 
77° F. under a load of 100 grams with a No. 2 needle at 5 seconds, when evap- 
orated at 500° F. in an open dish shall lose not less than 75.0 per cent. 

8. Adhesiveness: The adhesiveness at 77° F. by the Osborne test shall not be 
less than 400 seconds. 



* For the methods and results of tests of asphalts see Hubbard's Dust Preventives and 
Road Binders, 8vo, p. 416, John Wiley & Sons, New York, 1910; Richardson's Modern Asphalt 
Pavement, 8vo, p. 629, John Wiley & Sons, New York, 1908. 

t Letter to the author under date of July 13, 1917, 



278 



BITUMINOUS ROAD MATERIALS 



[chap. VIII 



537. Asphalt Binder for Bituminous Macadam. The American 
Society of Municipal Improvements on October 12, 1916, adopted 
restricted specifications for four kinds of asphalt, any one of which is 
acceptable as a binder for bituminous macadam. The full specifi- 
cations for an asphalt cement made from Gilsonite and asphaltic 
oil follow. The specifications for the three other asphalts are in 
exactly the sam.e form; and Table 31 gives the essential elements 
of the specifications of all four. . 



TABLE 31 

Comparison of Specifications for Asphalt Cements for Bituminous 

Macadam 

Standards of American Society of Municipal Improvements, Adpoted October 1, 1915 





Items. 


Kind of Asphalt Cement. 


Ref. 
No. 


Gilsonite 

and 

Asphalt Oil. 


Texas and 
California 
Oil Asphalt. 


Mexican Oil 
Asphalt. 


Bermudez 
Asphalt. 


1 




177° C. 

205° C. 

0.96-1.00 

100-120 

>50 
>60° C. 


177° C. 

205° C. 

1.00-1.03 

90-110 
>15 
>30°C. 


177° C. 

205° C. 

1.025-1.045 

110-130 

>30 
>40°C. 


177° C 


2 
3 
4 

5 


Flash point, not less than 

Specific gravity at 25° C 

Penetration — 

100 grams, 5 sec, 25° C 

200 grams, 60 sec, 40° C... 
Melting point by cube method . 

Viscosity by N. Y. float appa- 
ratus 


163° C. 
1.035-1.060 

130-160 
>30 

120-180 sec 


6 

7 

8 

9 

10 


Distillation, loss after 5 hrs 

Bitumen soluble in disulphide . . 
Bitumen soluble in tetrachloride 
Bitumen soluble in naphtha .... 


<2.0% 
99.5% 
99.5% 

75-85% 
8-12% 


<2.0% 
99.5% 
99.5% 

75-85% 
9-13% 


<2.0% 

99.5% 

99.5% 

70-80% 

12-17% 


<3.0% 
94-98.0 

98.5% 

75-85% 

11-14% 







538. Gilsonite and Asphaltic Oil. 1. Foam: The asphalt cement shall be 
homogeneous, free from water, and shall not foam when heated to 177° C. (350° F.) 

,2. Flash Point: It shall show a flash point of not less than 205° C. (400° F.) 
when tested in the New York State Board of Health Closed Oil Tester. 

3. Specific Gravity: Its specific gravity at a temperature of 25° C. (77° F.) 
shall be not less than 0.960 nor more than 1.000. 

4. Evaporation: When tested with a standard No. 2 needle by means of a 
standard penetrometer, it shall show penetrations within the following limits 
for the conditions stated, the penetrations being expressed in hundredths of a 
centimeter: 100-gram load, 5 seconds at 25° C. (77° F.), from 100 to 120; 200- 
gram load, 1 minute at 4° C. (39° F.), not less than 50. 

5. Melting Point: Its melting point as determined by the cube method shall 
be not less than 60° C. (140° F.). 

6. Distillation: When 50 grams of the material is maintained at a uniform 
temperature of 163° C. (325° F.) for 5 hours in an open cylindrical tin dish 5^ 
centimeters (about 2 \ inches) in diameter, with vertical sides measuring approx- 
imately 3| centimeters (about 1\ inches) in depth, the loss in weight shall not 
exceed 2.0 per cent of the original weight of the sample. 



ART. 1] ASiPHALT 279 

Penetration of Residue: The penetration of the residue when tested as de- 
scribed in paragraph 4 with a standard No. 2 needle under a load of 100 grams for 
5 seconds at 25° C. (77° F.), shall be not less than one half the penetration of the 
original material tested under the same condition. 

7. Bitumen Soluble in Bisulphide: Its bitumen as determined by its solu- 
bility in chemically pure carbon disulphide at room temperature, shall be not 
less than 99.5 per cent. 

8. Bitumen Soluble in Tetrachloride: It shall be soluble in chemically pure 
carbon tetrachloride at room temperature, to the extent of not less than 99.5 
per cent of its bitumen as determined by paragraph 7. 

9. Bitumen Soluble in Naphtha: It shall be soluble in 86 to 88° Baume 
paraffin naphtha, of which at least 85.0 per cent distills between 35° and 65° C. 
(95° and 149° F.), to the extent of not less than 75.0 per cent nor more than 85.0 
per cent of its bitumen as determined by paragraph 7. 

10. Fixed Carbon: It shall yield not less than 8.0 per cent nor more than 12.0 
per cent of fixed carbon. 

539. Asphalt Binder for Bitmninous Concrete. The American 
Society of Municipal Improvements on October 12, 1916, adopted 
restricted specifications for four kinds of asphalt any one of which is 
acceptable as a binder for bituminous concrete. The full specifi- 
cations for asphalt made of Gilsonite and asphaltic oil follow. The 
specifications for the four other materials are in exactly the same 
form. Table 32, page 280, gives the essential elements of the speci- 
fications of all five asphalts. 

540. Gilsonite and Asphalt Oil. 1. Foam: The asphalt cement shall be 
homogeneous, free from water, and shall not foam when heated to 177° C. 
(350° F.). 

2. Flash Point: It shall show a flash point of not less than 205° C. (400° F.) 

3. Specific Gravity: Its specific gravity at a temperature of 25° C. (77° F.) 
shall be not less than 0.970 nor more than 1.000. 

4. Penetration: When tested with a standard No. 2 needle by means of a 
Dow penetrometer (or other penetrometer giving the same results as the Dow 
machine), it shall show penetrations within the following limits for the conditions 
stated, the penetrations being expressed in hundredths of a centimeter: 100-gram 
load, 5 seconds, at 25° C. (77° F.), from 75 to 90; 200-gram load, 1 minute, at 
4° C. (39° F.), not less than 35; 50-gram load, 5 seconds, at 46° C. (115° F.) 
net more than 250. 

5. Melting Point: Its melting point as determined by the cube method shall 
be not less than 55° C. (131° F.). 

6. Evaporation: When 50 grams of the material is maintained at a uniform 
temperature of 163° C. (325° F.) for 5 hours in an open cylindrical tin dish, 5| 
centimeters (about 21 inches) in diameter, with vertical sides measuring approxi- 
mately 3^ centimeters (about 1^ inches) in depth, the loss in weight shall not 
exceed 1.0 per cent of the original weight of the sample. 

Penetration of Residue: The penetration of the residue, when tested as 



280 



BiftfMiNOtrS HOAD MATERIALS 



[chap. VIII 



described in paragraph 4 with a standard No. 2 needle under a load of 100 grams 
for 5 seconds at 25° C. (77° F.) shall be not less than one half the penetration of 
the original material tested under the same conditions. 

7. Bitumen Soluble in Bisulphide: Its bitumen as determined by its solu- 
bility in chemically pure carbon disulphide at room temperature shall not be 
less than 99.5 per cent. 

8. Bitumen Soluble in Tetrachloride : It shall be soluble in chemically pure 
carbon tetrachloride at room temperature to the extent of not less than 99.5 
per cent of its bitumen as determined by paragraph 7. 

9. Bitumen Soluble in Naphtha: It shall be soluble in 86 to 88° Baume par- 
affin naphtha, at least 85 per cent of which distills between 40 and 55° C. (104° 
and 131° F.), to the extent of not less than 70.0 per cent nor more than 80.0 
per cent of its bitumen as determined by paragraph 7. 

10. Fixed Carbon: It shall yield not less than 8.0 per cent nor more than 
12.0 per cent of fixed carbon. 



TABLE 32 ' 

Comparison op Specifications for Asphalt Cements for Bituminous 

Concrete 

Standards of American Society of Municipal Improvements, Adopted October 14, 1915 



Item. 



Shall not foam at 

Flash point, not less than, 

Specific gravity at 25° C. . 

Penetration — 100 grs. . . . 
—200 grams. . 

Melting point by cube 
method 

Viscosity by N. Y. float 
apparatus 

Evaporation, loss after 5 
hrs 

Bitumen soluble in disul- 
phide 

Bitumen soluble in tetra- 
chloride 

Bitumen soluble in naph- 
tha 

Fixed carbon 



Kinds of Asphalt. 



Gilsonite 

and Asphalt 

Oil. 



177° C. 

205° C. 

.97-1.000 

75-90 

>35 

> 55° C. 



<1.0% 

99 . 5% 

99.5% 

70-80% 
8-12% 



Texas Oil 
Asphalt. 



177° C. 

205° C. 

1 . 000-1 . 030 

90-100 

>30 

> 50° C. 



<1.0% 

99.5% 

99.5% 

72-78% 
11-15% 



California 
Oil Asphalt, 



177° C. 

205° C. 

1.030-1.040 

70-90 

>10 

>45° C. 



<2.0% 

99.5% 

99.5% 

80-88% 
10-14% 



Mexican 
Oil Asphalt, 



177° C. ' 

205° C. 

1.025-1.050 

85-95 

>20 

> 50° C. 



<2.0% 

99.5% 

99.5% 

67-77% 
12-18% 



Bermudez 
Asphalt. 



177° C. 

165° C. 

1.040-1.060 

140-160 

>40 



120-180 sec 

<3.0% 

93-98% 

98.5% 

75-85% 
11-15% 



541. Asphalt for Seal Coat for Bituminous Concrete. The 

American Society of Municipal Improvements adopted restricted 
specifications for three kinds of asphalt for the seal coat of bitumi- 
nous concrete pavements in which tar is the cementing material of 
the concrete. These specifications are of the same general form as 
those in § 538 and § 540. The essential elements of the specifi- 
cations are shown in Table 33. 



ART. 1] 



ASPHALT 



281 



TABLE 33 

Specifications for Asphalt for Seal Coat for Tar-concrete Pavements 

Standards of American Society of Munislpal Improvements, Adopted October 14, 1915 



Ref. 
No. 



Items. 



Kinds of Asphalt. 


Gilsonite 


Texas Oil 


Mexican 


and 


Asphalt. 


Oil Asphalt. 


Asphalt Oil. 






177° C. 


177° C. 


177° C. 


205° C. 


205° C. 


205° C. 


1.025-1.050 


1.030-1.045 


1.025-1.055 


85-95 


60-70 


60-70 


>20 


>18 


>16 


50° C. 


60° C 


55° C. 


<2.0% 


<1.0%, 


<i.o% 


>50% 


>50% 


>50% 


99.5% 


99.5% 


99.5% 


99.5% 


99.5% 


99.5 % 


70-80% 


70-80% 


67-77% 


8-12 


12-16 


13-18 



Shall not foam at 

Shall not flash at 

Specific gravity at 25° C 

■Penetration — 100 grams 

200 grams 

Melting point by cube method 

Distillation, loss after 5 hours 

Penetration of residue, per cent of original 

Bitumen soluble in disulphide 

Bitumen soluble in tetrachloride 

Bitumen, per cent of total soluble in naphtha. . . 
Fixed carbon, per cent 



542. Asphalt for Sheet Asphalt Pavements. The following are 
the specifications of the American Society of Municipal Improve- 
ments, adopted October 14, 1915, for asphalt cement for sheet asphalt 
and asphalt concrete pavements: 

1. Homogeneous: The asphalt cement shall be thoroughly homogeneous. 

2. Penetration: It shall have a penetration at 77° F. of from 30 to 55 for 
heavy traffic streets, and 55 to 85 for light traffic streets, depending upon the sand 
and asphalt used and the local climatic conditions. 

3. Flash Point: It shall not flash below 350° F. when tested in a closed oil 
tester. 

4. Evaporation: When 20 grams of the asphalt cement are heated for 5 
hours at 325° F. in a tin box 2^ inches in diameter and f of an inch deep, after 
the manner officially prescribed, the loss shall not exceed 5 per cent by weight; 
and the penetration, at 77° F., of the residue left after such heating must not be 
less than one half the penetration, at 77° F., of the original sample before heating. 

5. Ductility: Either the asphalt cement or its pure bitumen when made 
into a briquette in the Dow mold shall have at 50 penetration at 77° F., a duc- 
tility of not less than 30 centimeters, when the two ends of the briquette are 
pulled apart at the uniform rate of 5 centimeters per minute. 

When the asphalt cement as used has ^ penetration other than 50 at 77° F., 
an increased ductiHty of 2 centimeters will be required for every 5 points in pen- 
etration above 50; and a corresponding allowance will be made for a penetration 
below 50. 

543. There a.re two marked differences between the preceding 
specifications and those for asphalt binder for bituminous macadam 
(§ 538) and those for asphalt binder for bituminous concrete (§ 540). 

In the first place, the preceding specifications are briefer, having 
only five items while the others have ten; but the longer specifica- 



282 BITUMINOUS ROAD MATERIALS [CHAP. VIII 

tions contain several items of only minor importance. For example, 
the foam test determines only the presence of water, but determines 
nothing concerning the quality of the asphalt. Again, the specific 
gravity test is of value in identifying the asphalt, but is of no value 
in determining its quality. Further, the melting point indicates 
consistency, which is more accurately determined by the penetration 
test. On the other hand, notice that the specifications of § 542 alone 
contain a test for ductility, which is the sole test to determine the 
cementing value of the asphalt. 

In the second place, the specifications of § 542 are the general or 
blanket form, while those of § 538 and § 540 are restricted or special 
form. For a discussion of the merits of the two forms, see § 532. 

544. Asphalt Filler for Block Pavements. It is important that 
the asphalt used as a filler in block pavements shall be affected as 
little as possible by temperature changes; and therefore the manu- 
facturers have prepared a material especially for this purpose, 
partly by refining the asphalt and partly by hardening it by oxidation, 
i. e., by passing air through it. The following are the usual speci- 
fications for an asphalt filler for brick, stone-block, and wood-block 
pavements.* 

The asphalt paving cement shall be obtained by the distillation of an as- 
phaltic petroleum at a temperature not exceedidg 700° F., and shall comply 
with the following requirements: 

1. It shall be homogeneous. 

2. The melting point shall not be less than 130 nor more than 145° F. 

3. The solubility in carbon tetrachloride shall not be less than 98| per 
cent. 

4. The penetration at 77° F. shall not be less than 60 nor more than 100; 
and the penetration at 100° F. shall not exceed three times the penetration at 
77° F. The contractor before beginning work shall obtain from the engineer a 
statement in writing as to the penetration desired, and a variation not greater 
than ten points either way from this penetration will be permitted. 

5. The ductility at 77° F. shall not be less than 40 centimeters, the rate of 
elongation being five centimeters per minute. 

6. It shall not lose more than 3 per cent by volatilization when maintained 
at a temperature of 325° F. for 5 hours; nor shall the penetration of the residue 
after such heating be less than one half the original penetration. 

7. The asphalt filler shall be used on the work at a temperature of not 
less than 275° F.; and shall at no time be heated above 350° F. 

8. It shall be delivered where directed by the engineer in time to allow for 
examination and analysis. 

♦Specifications for Stone Block Paving, adopted by American Society of Municipal Im- 
provements, 1916. 



ART. 2] 



PETROLEUM 



283 



545. Cost. The cost of all materials is abnormal at present 
owing to the Great European War; but the asphalt market is further 
disturbed by the unsettled political conditions in Mexico, which 
make it difficult to obtain Mexican petroleum for fluxing. The 
prices of solid refined asphalt for January, 1917, which prices 
obtained for the year 1917, f.o.b. Maurer, N. J., in tank cars, were 
about as follows : 



Kinds of Asphalt. 


Price per Ton 
(2000 Lb.) 


Per Cent 
Bitumen. 


Value for 

100 Per Cent 

Bitumen. 


Bermudez 


$27.00 
15.00 
16.00* 
18.00 
19.00 


95.0 
95.5 

98.8 
99.5 


S25 . 65 


Mexican. 


14.32 


Residual 




Texas. 


17.78 


Trinidad 


18.90 











* Varies $3.00 to $4.00 either way in different parts of the country. The average price has 
advanced 100 per cent since 1914. 

If asphalt is bought in barrels or drums, the cost is usually 1.5 
to 2 cents per gallon more than above, with sometimes a little rebate 
on the returned barrels. 

Liquid asphalt is now (1917) 7 cents per gallon f.o.b. Maurer, N. J. 

546. For current prices of asphalts, consult the price Usts in the 
technical journals. 

Art. 2. Petroleum 

547. Classification. There are two types of crude petro- 
leum — one giving a paraffin residue, and the other an asphalt 
residue. The petroleimas from Pennsylvania, Ohio, Indiana and 
Illinois have a paraffin residue or base; while those from California 
and Mexico and some from Texas have an asphaltic base. The 
oils from Kentucky, Louisiana, and some from Texas have a mixed 
paraffin and asphalt base, and are usually called semi-asphaltic oils. 

The oils having a paraffin base are more or less greasy, and have 
no binding qualities, but rather a lubricating effect; and are useful 
only as a temporary dust layer. The oils having an asphaltic or 
bituminous base are more valuable for roads, since the bituminous 
base binds the particles of the road together, even after the more 
volatile portions of the oil have evaporated. 

Crude petroleum as it comes from the well is an oily liquid, vary- 
ing in color from greenish brown to nearly black, and varying in 
specific gravity from 0.73 to 0.97. In the refining process the more 



284 



BITUMINOUS ROAD MATERIALS 



[chap. VIII 



volatile and* more valuable constituents, as benzine, gasoline, kero- 
sene, and lubricating oils, are driven off by heat. It is the residue 
that is used in oiling roads and as a flux for softening the solid native 
asphalts (§ 528-29). The character of the residue varies with the 
crude petroleum and with the process of refining, and its value for 
road purposes depends upon its specific gravity and the amount of 
bitumen it contains. 

548. Methods of Refining. There are two methods of 
refining petroleum to produce materials for use on roads. One 
method is that of ordinary distillation by the use of external heat, 
usually steam. The distillation is carried on until only the solid or 
semi-sohd portion remains. This method is not usually applied 
to paraffin petroleums on account of the high temperatures necessary 
and the resulting decomposition. 

The second method consists in blowing atmospheric air through 
petroleum heated to a temperature below that required for distilla- 
tion. The air produces oxidation and condensation of the lighter 
hydrocarbons, and the oil gradually thickens. This method is 
usually applied to oils having a paraffin base; and the residue is 
known as blown oil, or sometimes as blown-oil asphalt, although it is 
usually paraffin or at most a semi-asphalt mixture. 

549. Shipping the Oil. Road oil is usually shipped in tank 
cars holding either 4000 to 6000 gallons or 8000 to 10,000 gallons, the 
latter being much more conomon. Oil may be had in barrels; but it 
is then more expensive, and is also much more difficult to handle. 
The tank cars are equipped with steam heating coils, so the material 
may be heated in the tank by attaching a steam pipe or hose. 

There are a number of simple pumps on the market that will 
pump either hot or cold oil. The ordinary thresher's water-tank 
pump may be used for pumping cold oil; but not hot oil, as it will* 
soon burn out the valves. Fig. 92, page 285, shows the method of 
pumping road oil from the dome of a tank car by means of a hand 
diaphragm pump; and a thresher's water-tank pump may be used 
in the same way. However, this method is nearly obsolete, since 
state and county highway departments usually own outfits made 
particularly for this purpose. 

Power-driven diaphragm and rotary pumps are the forms gen- 
erally used ; and are attached to the outlet in the bottom of the tank 
car. These pumps are driven by an independent gasoline engine or 
by steam from a steam road-roller, which is sometimes needed at the 
tank car to supply steam to heat the oil. Fig. 93 shows the method 



ART. 2] 



PETROLEUM 



285 



of transferring road oil from the tank car to the distributing 
wagon by means of a gasoHne-driven rotary pump. 

550. ASPHALTIC Content of Road Oils. Road oils are fre- 
quently referred to as containing a certain per cent of. asphalt; 
and the oil refineries always classify road oils according to their 
asphaltic content — see § 561. 

This " asphalt '' is not a definite compound that can be deter- 
mined by chemical analysis. To determine the " asphalt " in a road 
oil, the oil is heated in a closed oven to a temperature of 400° F., 
which drives off the Hght or volatile constituents and leaves a semi- 




FiG. 92.- 



-Unloading Oil with Diaphragm 
Pump. 



Fig. 93. — Unloading Oil with Rotary 
Pump. 



solid or solid residue. This residue is called asphalt, although 
it may contain many different bitumens. If the residue is paraffin, 
it is useful as a dust layer, but worthless as a road binder. Since road 
oil is so cheap, it is not likely that the residue contains any adulter- 
ation. The amount of residue in a road oil gives no indication of its 
value for use on a road, since the residue may be wholly paraffin, or 
semi-asphalt, or asphalt. However, the per cent of " asphalt " does 
give some indication as to the viscosity of the oil, i. e., as to the 
amount of body it contains. The method employed and equipment 
used in determining the amount of " asphalt " vary considerably, 
and are not usually stated; hence the result is quite indefinite. No 
reliance should be placed upon such a loose term; but the oil should 
be bought to conform to definite specifications. 

The degree of hardness of this residue is measured by the depth 
of penetration of a No. 2 needle under a load of 100 grams in 5 seconds. 
It is sometimes specified that the road oil shall contain a certain per 
cent of '' asphalt " having a stated penetration. For example: 
" The oil shall contain 90 per cent of ' asphalt ' having a penetration 
of 80." 



286 BITUMINOUS ROAD MATERIALS fCHAP. VIII 

551. Specifications for Road Oil. Road oils are usually 

bought without any specifications as to tlieir composition and also 
without inspection or analysis. This is very unfortunate, since the 
residue may be paraffin, which is a lubricant rather than a binder; 
and also since the residue, even though a bitumen, may have been 
burned in the refining process until it possesses Httle or no binding 
qualities. 

Specifications differ considerably according to the purpose for 
which the oil is to be used or the conditions under which it is applied; 
and practice has not yet established a standard for any particular 
purpose or condition. Below are the specifications of several grades 
of road oil that have been successfully used. 

552. For Park Drives. The following are the specifications of 
the light oil used as a dust layer (§ 330), in Washington, D. C, on 
gravel park drives.* 

1. The oil shall be a viscous fluid product, free from water, and showing 
some degree of adhesiveness when rubbed between the fingers. 

2. It shall have a specific gravity of not less than 0.940 at 25° C. 

3. It shall be soluble in carbon disulphide at air temperature to at least 99 
per cent; and shall not contain over 0.2 per cent of insoluble inorganic matter. 

4. It shall contain not less than 3 per cent nor more than 10 per cent of 
bitumen insoluble in 86° parafiin naphtha at air temperature. 

5. When 240° c.c. of the oil is heated in an Engler viscosimeter to 50° C. 
and maintained at this temperature for at least 3 minutes, the first 50 c.c. shall 
flow through the aperture in not less than 10 minutes nor more than 20 minutes. 

6. When 20 grams of the material is heated for 5 hours in a cylindrical tin 
dish, approximately 2| inches in diameter by 1 inch high, at a constant tem- 
perature of 163° C, the loss in weight by volatilization shall not exceed 20 per 
cent. The residue should be decidedly sticky. 

7. Its fixed carbon shall not be less than 3.5 per cent. 

553. For Earth Roads. The two following specifications have 
been adopted by the Illinois Highway Department, f and have prac- 
tically been adopted by nearly all State Highway Departments for 
the surface treatment of earth roads. The oils are to be tested 
according to the method described in Bulletin No. 314, U. S. Depart- 
ment of Agriculture, December 10, 1915. 

554. For Loam and Clay. The following light oil should be ap- 
pHed cold, for a first application on loam or clay. For subsequent 
applications use the oil as described in the next section. 

* Paper by Col. Spencer Cosby, U. S. Army, in charge of Buildings and Grounds, Washing- 
ton, D. C, presented before Section D of the American Association for Advancement of Science, 
December 29, 1911. 

I Private letter fr9in "W"t W. M^TX, Chief Highway Engineer, under date of July 18, 1917. 



AET. 2] PETROLEtJM 287 

1. The oil shall be homogeneous and free from water. 

2. Specific Gravity 25° C. (77° F.) not less than 0.890 

3. Bitumen soluble in disulphide not less than 09.5% 

4. Residue of 100 penetration * 40 to 60% 

5. Specific viscosity at 40° C. (104° F.) 10.0 to 25.0 

When it is desired to apply the oil hot, oils somewhat more viscous and having 
a specific viscosity at 40° C. (104° F.) up to 50 will be acceptable, provided 
these oils conform to the requirements of the specifications in all other respects. 
An oil having a specific viscosity at 40° C. (104° F.) of more than 25.0 will not be 
accepted, unless it is to be applied hot. 

555. For Sandy Soil. The following oil should be applied cold, 
and is suitable for a dust layer on a sandy earth road, for a second 
application on a loam or clay road, and also for a surface application 
on a water-bound gravel or macadam road. 

1. The oil shall be homogeneous and free from water. 

2. Specific gravity at 25° C. (77° F.) .not less than 0.910 

3. Specific viscosity at 40° C. (104° F.) 10.0 to 25.0 

4. Loss at 163° C. (325° F.) for 5 hours not over 25% 

5. Bitumen soluble in disulphide ; not less than 99.5% 

6. Bitumen insoluble in 86° B. naphtha not less than 5% 

7. Fixed carbon not less than 4.0% 

8. Specific viscosity at 40° C. (104° F.) 10.0 to 25.0 

When it is desired to apply the oil hot, oils somewhat more viscous and 
having a specific viscosity of 40° C. (104° F.) up to 50 will be acceptable, pro- 
vided these oils conform to the requirements of the specifications in all other 
respects. An oil having a specific viscosity at 40° C. (104° F.) of more than 25.0 
will not be accepted unless it is to be applied hot. 

556. For Water-bound Gravel or Macadam. The three following 
specifications have been adopted by the Illinois Highway Department f 
for a dust layer and a protective coating on water-bound gravel or 
macadam roads, and practicallj^ the same have been adopted by 
most of the State Highway Departments. The oils are to be tested 
according to the methods described in Bulletin No. 314, U. S. Depart- 
ment of Agriculture, December 10, 1915. 

The light oil (§ 557) is preferable for the first application or where 
the road is somewhat dusty, since it penetrates better than the 
heavier oils; but for subsequent applications a heavier oil (§ 558 or 
§ 559) is preferable. If the gravel or macadam is very clean, the 
heavier oil may be used for a first application. 

* Am. Soc. Test. Mat. Standard Test, D-5-16. 

t Private letter from W. W. Marr, Chief Highway Engineer, under date of Jxily 18, 1917. 



288 BiTtJMlNOtJS ROAD MATERIALS [cHAP. Vlll 

557. Light Oil. The following oil is to be applied cold. 

1. The oil shall be homogeneous and free from water. 

2. Specific gravity 25° C. (77° F.) 0.920 to 0.970 

3. Loss at 163° C. (325° F.) for 5 hours 20.0% to 30.0% 

4. Bitumen soluble in disulphide not less than 99.5% 

5. Bitumen insoluble in 86° B. naphtha 5.0 to 20.0% 

6. Fixed carbon 4.0% to 10.0% 

7. Specific viscosity at 25° C. (77° F.) 30.0 to 70.0 

558. Medium Oil. The following oil need not be applied hot 
except when the temperature of the air is below 80° F. 

1. The oil shall be homogeneous, free from water, and shall not foam when 

heated to 100° C. (212° F.). 

2. Specific gravity 25° C. (77° F 0.960 to 1.010 

3. Flash point not less than 100° C. (212° F.) 

4. Float test at 32° C. (90° F.) 30 to 90 seconds 

5. Loss at 163° C. (325° F.) for 5 hours not over 15.0% 

6. Float test of residue at 50° C. (122° F.) 90 to 180 seconds 

7. Bitumen soluble in disulphide not less than 99.5% 

8. Bitumen insoluble m 86° B. naphtha 7.0 to 20.0% 

9. Fixed carbon 5.0% to 10.0% 

10. Specific viscosity at 100° C. (21,2° F.) 5.0 to 15.0 

559. Heavy Oil. The following oil should be applied hot. 

1. The oil shall be homogeneous, free from water, and shall not foam when 

heated to 150° C. (302° F.) 

2. Specific gravity 25° C. (77° F.). . not less than 0.980 

3. Flash point not less than 150° C. (302° F.) 

4. Float test at 50° C. (122° F.) 100 to 200 seconds 

5. Loss at 163° C. (325° F.) for 5 hours, not over 5.0% 

6. Float test of residue at 50° C. (122° F.) 120 to 240 seconds 

7. Bitumen soluble in disulphide not less than 99.5% 

8. Bitumen insoluble in 86° B. naphtha 10.0 to 25.0% 

9. Fixed carbon. 7.0% to 15.0% 

10. Specific viscosity at 100° C. (212° F.) . . ; 30.0 to 70.0 

560. Cost. The price of road oils varies greatly, partly because 
of the natural variation with locality, but chiefly because a large 
proportion of road oils is sold without specifications or inspection. 
The demand for oil for road purposes has increased so rapidly in 
recent years that the price has advanced more rapidly than most 
construction materials. 

561. The following are the market quotations in Engineering 
News-Record, July 5, 1917. The prices are for road oil in tank cars 
(8000 gallons minimum capacity) f.o.b. places named. 



ART. 3] TAR 289 

New York City, 40-50 per cent asphalt 6^ cts. per gal 

60-70 per cent asphalt 7 cts. per gal 

dust layer 7| cts. per gal 

binder 8| cts. per gal 

St. Louis, asphalt 5 cts. per gal 

Dallas, 40-50 per cent asphalt 6 cts. per gal 

60-70 per cent asphalt 7^ cts. per gal 

San Francisco, 75-79 per cent asphalt (barrel = 42 gal.) $1.83 per bbl 

Art. 3. Tar 

563. The tar used in road work is obtained as a by-product in 
the destructive distillation of bituminous coal in the manufacture 
of illuminating gas or in the production of coke, as well as in the 
decomposition of petroleum. 

564. Definitions. Coal Tar. Tar produced from the destruc- 
tive distillation of coal. 

Coke-oven Tar. A by-product in the manufacture of coke. 

Gas-house Tar. A by-product in the manufacture of illuminating 
gas from coal. 

Oil-gas Tar. A by-product in the manufacture of illuminating 
gas from petroleum. 

Pitch. The solid residue produced by the evaporation or dis- 
tillation of tar. 

Refined Tar. A tar freed from water by evaporation or dis- 
tillation, which process is continued until the tar is of the desired 
consistency. When all the water is driven off, it is called Dehydrated 
Tar. Refined tar is also produced by fluxing the tar residuum with a 
tar distillate, in which case the product is called Cut-back Tar. 

Water-gas Tar. A by-product in the manufacture of carbureted 
water-gas from petroleum. 

565. CHARACTERISTICS OF Tar. Most of the tar used in road 
work is coal tar, either coke-oven or gas-house tar. In some partic- 
ulars the characteristics of tars overlap; but the following table shows 
their chief differences: 

characteristics. kind of TAR: 

CoKE-OvEN. Gas-House. 

Water, per cent 2.2 2.9 

Light oil up to 200° C 3.4 4.0 

Creosote oil, per cent 14 . 5 8.6 

Naphthalene, crude, per cent 6.7 7.4 

Anthracene, crude, per cent 27.3 17.4 

Pitch, per cent 44.3 58.4 

Free carbon, per cent 5-8 15-25 



290 



BITUMINOUS ROAD MATERIALS 



[chap. VIII 



The quality of gas-house tar depends upon the temperature at 
which the distillation takes place. The distillation usually takes 
place at a high temperature; and consequently the tar contains less 
of the heavy oils and more of the solid bitumen and more free carbon, 
and is not desirable for road work, because of an excess of free carbon 
and of the lack of the heavy oils. 

Coke-oven tar is usually formed at a lower temperature, and 
hence contains more of the heavy oils and less free carbon; and is 
therefore usually more suitable for road work than gas-house tar. 

Water-gas tar is hghter than coal tar, contains a larger percentage 
of heavy oils, and a less percentage of pitch. It is usually low in free 
carbon, and does not contain ammonia. Since water-gas tars con- 
tain comparatively small proportions of pitch, they are not as suitable 
for a road binder as coal-gas or coke-oven tars; but since they con- 
tain a larger percentage of the heavier oils, they are desirable materials 
for use as dust layers. 

566. Crude tar is refined by driving off the Hghter oils. The 
residue may be liquid or soHd according to the temperature to which 
the distillation was carried and the extent to which the heavy oils 
have been removed. Sometimes the distillation is carried only far 
enough to drive off the water and the hghter oils. Such a product is 
known as dehydrated tar; and it is more suitable for road work 
than crude tar, since it contains no water or ammonia. 

567. Shipping Tar. Tar is shipped in barrels or metal drums 
or in tank cars; and is unloaded and distributed the same as asphalt 
and oil — see § 504 and § 549. 

568. Specifications for Tar. Practice has not estabhshed 
standard specifications ; and consequently there are a great number 
in use, which differ according to the source or character of the tar 
and also according to the opinion of the one writing the specifica- 
tions. Only an expert road engineer and chemist should attempt 
to prepare specifications; and then great care is necessary, since a 
limitation in one particular may affect the limits of some other 
factor. The producers of bituminous materials make a variety of 
grades of material, which are sold under different trade names 
(see § 578). 

Below are the specifications for materials that have been suc- 
cessfully used for different kinds of work by good authorities. 

569. For Bituminous Surfaces. The two following specifications 
have been adopted for refined tar for bituminous surfaces on water- 
bound gravel or macadam roads (Chapter IX), and on bituminous 



AET. 3] TAR 291 

bound roads (Chapter X) by the lUinois Highway Department,* 
and are practically the same as those adopted by most State Highway 
Departments. The tests are to be made as described in Bulle- 
tin 314, U. S. Department of Agriculture, December 10, 1915. 

For the first treatment of a road the hght tar of § 570 is to be pre- 
ferred; and for subsequent apphcation the heavier tar of § 571 is 
better. 

570. Hot Application. The following tar should be applied 
hot. 

1 . The tar shall be homogeneous and free from water. 

2. Specific gravity 25° C. (77° F.) 1.120 to 1.200 

3. Specific viscosity at 40° C. (104° F.) 4.0 to 12.0 

4. Total distillate by weight :t 

to 170° C. (338° F.) not over 5.0% 

to 300° C. (572° F.) not over 35.0% 

5. Specific gravity of total distillate 25° C. (77° F.) not less than 1.010 

6. 'Melting point of residue not over 65° C. (149° F.) 

7. Bitumen soluble in disulphide 88.0 to 96.0% 

8. Inorganic matter (ash) not over 0.5% 

571. Cold Application. The following tar should be apphed 
cold. 

1. The tar shall be homogeneous and free from water. 

2. Specific gravity 25° C. (77° F.) 1.180 to 1.250 

3. Float test 32° C. (90° F.) 90 to 150 seconds 

4. Total distillate by weightif to 180° C. (338° F.) not over 1.0% 

to 300° C. (572° F.) not over 25.0% 

5. Specific gravity of total distillate, 25° C. (77° F.) not less than 1.030 

6. Melting point of residue not over 75° C. (167° F.) 

7. Bitumen soluble in disulphide 78.0 to 88.0% 

8. Inorganic matter (ash) not over 0.5% 

572. For Bituminous Macadam. The American Society of 
Municipal Improvements on October 12, 1916, adopted standard 
specifications for two grades of tar for bituminous macadam roads 
(Art. 1, Chapter X), which materials are optional with each other 
and also with any of the four kinds of asphalt described in § 537-38 
and Table 31, page 278. The specifications in full for water-gas tar 
are given in § 573; and Table 34 shows the essential features of 
both tars. 



* Private letter from W. W. Marr, Chief Highway Engineer, under date of July 18, 1917, 
t Amer. Soc, Test, Mat, Standard Test, D-20-16. 



292 



BITUMINOUS ROAD MATERIALS 



[chap. VIII 



573. Water-gas Tar.* 1. Foam: Refined water-gas tar shall be homogene- 
ous, free from water, and shall not foam when heated to 121° C. (250° F.). 

2. Specific Gravity: The specific gravity at a temperature of 25° C. (77° F.) 
shall be not less than 1.150 nor more than 1.200. 

3. Viscosity: When tested by means of the New York Testing Laboratory 
Float Apparatus, the float shall not sink in water maintained at 50° C. (122° F.) 
in less than 120 nor more than 150 seconds. 

4. Bitumen Soluble in Bisulphide: The bitumen as determined by its solu- 
bility in chemically pure carbon disulphide at room temperature, shall be not less 
than 95.0 per cent; and the material insoluble in carbon disulphide shall not show 
more than 0.2 per cent ash upon ignition. 

5. Distillation: When distilled according to the tentative m^ethod recom- 
mended by Committee D-4 of the American Society for Testing Materials in 
1911, it shall yield not more than 0.5 per cent distillate at a temperature 
lower than 170° C. (338° F.); not more than 12.0 per cent shall distill below 
270° C. (518° F.); and not more than 25.0 per cent shall distill below 300° C. 
(572° F.). 

6. Distillate, specific gravity of: The total distillate from the test made in 
accordance with paragraph 5 shall have a specific gravity at a temperature of 
25° C. (77° F.) of not less than 0.980 nor more than 1.020. 

7. Distillate, melting point of: The melting point, as determined in water 
by the cube method, of the pitch residue remaining after distillation to 300° C. 
(572° F.) in accordance with the test described in paragraph 5, shall be not more 
than 75° C. (167° F.) 

TABLE 34 
Comparison of Specifications for Tars for Bituminous Macadam 

Standards of American Society of Municipal Improvements, Adopted October 12, 1916 



Ref. 

No. 


Items. 


Water-gas Tar. 


Coal Tar. 


1 


Shall not foam at 


121° C. 

1 . 150-1 . 200 

120-150 sec. 

95.0% 

0.5% 

12.0% 

25.0% 

0.98-1.020 

75° C. 


121° C. 


2 


Specific gravity at 25° C 


1.180-1.300 


3 

4 
5 

6 


Viscosity by N. Y. float apparatus 

Bitumen soluble in disulphide, not less than . . 
Distillation, yield to 170° C, not more than. 
Distillation, yield to 270° C, not more than. 
Distillation, yield to 300° C, not more than. . 
Distillate total, specific gravity of . 


150-180 sec. 

80.0-95.0 

0.5% 

10.0% 

20.0% 

1.020 


7 


Residue, melting point of, not more than .... 


. 75° C. 



574. For Bituminous Concrete. The American Society of 
Municipal Improvements on October 12, 1916, adopted standard 
specifications for two grades of tar suitable for the binder of bitumi- 
nous concrete (see Art. 2 of Chapter X), which materials are optional 
to each other and also with any one of the five V^des of asphalt 



* Specifications for Broken Roads with Bituminous Surface, adopted by American Society 
of Municipal Improvements, October 12, 1916, p. 24-25. 



ART. 3] 



TAR 



293 



described in § 540, and Table 32, page 280. The specification in 
full for one of the tars is given in § 575; and the essential features of 
both are shown in Table 35. 

575. Water-gas Tar. 1. Foam: The refined tar shaJl be homogeneous, free 
from water, and shall not foam when heated to 150° C. (302° F.). 

2. Specific Gravity: Its specific gravity at a temperature of 25° C. (77° F.) 
shall not be less than 1.160 nor more than 1.200. 

3. Viscosity: When tested by means of the New York Testing Laboratory 
Float Apparatus, the float shall not sink in water maintained at. 50° C. (122° F.) 
in less than 140 seconds nor more than 170 seconds. 

4. Bitumen Soluble in Bisulphide: The bitumen as determined by its solu- 
bility in chemically pure carbon disulphide at room temperature shall be not less 
than 95.0 per cent; and the material insoluble in carbon disulphide shall show 
nor more than 0.2 per cent ash upon ignition. 

5. Distillation: When distilled according to the tentative method recom- 
mended by Committee D-4 of the American Society for Testing Materials in 
1911, it shall yield no distillate at a temperature lower than 170° C. (338° F.); 
not more than 7.0 per cent by weight shall distill below 270° C. (518° F.); and 
not more than 20.0 per cent by weight shall distill below 300° C. (572° F.). 

6. Distillate, specific gravity of: The total distillate from the test made in 
accordance with paragraph 5 shall have a specific gravity at a temperature of 
25° C. (77° F.) of not less than 1.000 nor more than 1.020. 

7. Distillate, melting point of: The melting point, as determined in water by 
the cube method, of the pitch residue remaining after distillation to 300° C. 
(572° F.), in accordance with the test described in paragraph 5, shall be not 
more than 75° C. (167° F.). 

TABLE 35 

Comparison of Specifications for Tars for Bituminous Concrete 

Standards of American Society of Municipal Improvements, October 14, 1916 



Ref. 
No. 


Items. 


Water-gas Tar. 


Coal Tar. 


1 


Shall not foam at. 


150° C. 

1 . 160-1 . 200 

140-170 sec. 

95.0% 

0.0 

7.0% 

20.0% 

1.00-1.020 

75° C. 


150° C 


2 


Specific gravity at 25° C 

Viscosity by N. Y. float apparatus. 


1.200-1.300 
140-170 sec 


4 
5 

6 


Bitumen soluble in disulphide, not less than. . 

Distillation, yield to 170° C, not more than. . 

" 270° C, not more than. . 

/' " 300° C, not more than.. 

Distillate, total, specific gravity of 


75.0-90.0% 

0.0 

10.0% 

20.0% 

1 030 


7 


Distillate, residue, melting point of, not more 
than 


75° C. 



576. For Joint Filler of Block Pavements.* The following are the 
specifications for a tar suitable for the joint filler of brick, stone- 



* p. p. Sharpies, Manager and Chief Chemist, Tarvia Department, Barrett Manufacturing 
Co., forwarded for this use under date of July 13, 1917. 



294 BiTtJMINOUS ROAD MATERIALS [cHAP. VIlI 

block, or wood-block pavements. The specifications may need a 
slight variation for the extremes of northern or southern portions of 
this country. 

677. 1. Pitch. The pitch shall be straight-run residue from the distillation of 
coal tar. 

2. Specific Gravity: The specific gravity at 78° F. shall not be less than 1.24 
nor more than 1.32. 

3. Melting Point: The melting point shall not be lower than 115° F. nor 
higher than 150° F. For mastic filler the melting point shall be 115 to 135° F.; 
for brick and stone-block 125 to 140° F. ; and for wood-block, 140 to 150° F. 
The contractor before beginning work on any contract shall obtain from the 
Chief Engineer in writing a statement as to the melting point desired for that 
particular contract, and a variation of 5° F. either way from this value will be 
permitted; but the melting point must be within the limits indicated above. 

The melting point should be higher, the steeper the grade. For grades 
above 10 per cent, in a warm cHmate, the melting point should be 140° to 
150° F. 

4. Free Carbon: The free carbon shall not be less than 22 per cent nor more 
than 37 per cent. 

5. Distillation: The specific gravity of the distillate to 670° F. shall be not 
less than 1.07 at 140° F. compared with water at the same temperature. 

578. Trade Names. A trade name is in a sense a specification 
for a material; and hence the following definitions of well-known 
trade names for tar products are appropriate here : 

Tarvia A. A refined coal tar for hot surface application to macadam roads 
for preserving them and laying dust. Tarvia A in distinction from Tarvia B 
forms a perceptible blanket on the surface; and is therefore hmited for successful 
use to roads receiving either wholly automobile traffic or a high percentage of 
such trafiic. It has been largely used in park work in the neighborhood of large 
cities. 

Tarvia B. A refined coal tar for cold surface appHcation as a dust layer 
and road preservative. Primarily for use on macadam roads, but also applicable 
to gravel and other hard-surfaced roads. 

Tarvia KP. A refined coal-tar binder cut back to permit its use cold in 
making patches and in other maintenance work on bituminous surfaced and 
bituminous bound roads. 

Tarvia MF. A refined coal tar prepared for use as a mastic with sand in 
filling the joints of brick, stone-block, and lug wood-block pavements. 

Tarvia X. A refined coal tar prepared for use as a binder for bitimiinous 
macadam roads. Modifications are made to permit its use in bituminous con- 
crete. 

Tarvia XC. A Tarvia X prepared for use in patching and maintaining the 
joints in concrete roads. 

579. Cost of Road Tar. Cost data are always difficult to 
handle in printed matter, since the record is liable to be out of date 



ART. 3] 



TAR 



295 



before it is presented to the public; and this seems to be specially 
true of tar, particularly at the time this paragraph is written. 

The cost of road tars meeting the preceding specification, in 
the Middle and Eastern States where the conditions are more uniform 
than in other parts of the country, range from 8 to 13 cents per gallon 
f.o.b. siding at destination. The lighter materials suitable for cold 
application cost 1 or 2 cents per gallon less than those applied hot. 

580. For more recent data consult the price reports in the current 
technical journals. 



CHAPTER IX 
BITUMINOUS SURFACES FOR ROADS 

582. Before the advent of motor-driven vehicles gravel and mac- 
adam roads gave good service; but the coming of the automobile 
introduced new conditions that made necessary a radical change in 
the construction of a gravel or macadam road having any considerable 
proportion of motor-driven traffic. The low-hung swift-moving 
automobile, more than horse-drawn vehicles, throws the stone dust 
into the air and thus permits it to be blown away, and besides the 
rubber tires, unhke steel tires and horse shoes, do not make any 
stone dust to replace that blown away. Therefore gravel and mac- 
adam roads rapidly deteriorate under any considerable motor-driven 
traffic. This state of affairs led to the introduction, in substantially 
the past ten years, of several new forms of road construction in 
which the binding power of clay or stone dust is replaced by that of a 
bituminous material hke tar. 

There are two general types of such construction, viz.: one in 
which a superficial coating of bituminous material is laid upon a 
gravel, macadam or concrete road, or even upon a brick or stone- 
block pavement; and the other in which the bituminous material is 
employed as a binder for the upper stratimi of the road. The super- 
ficial layer is called a Protective Coating or a Bituminous Carpet, 
according to its thickness and construction. This type of con- 
struction mil be considered in this chapter. 

When the second form of construction is employed the road is 
known as either a Bituminous-Macadam or a Bituminous-Concrete 
Road, according to the details of the construction, which types of 
construction will be considered in the next chapter. 

583. Kinds of Bituminous Surfaces. The bituminous sur- 
face may consist either of a thin bituminous film or of a compara- 
tively thick mat composed of successive layers of bituminous 

296 



ART. 1] PROTECTIVE COATING 297 

material and screenings, sand or gravel. The former is usually called 
a Protective Coating, and the latter a Bituminous Carpet. 

Art. 1. Protective Coating 

584. A Ught oil is sometimes appHed to an earth road, a gravel 
road, or a water-bound macadam road to lay the dust. It is not 
expected that the oil will have smy binding power; and frequent 
applications are necessary for effectiveness. But when a water- 
bound gravel or macadam road is required to carry only a small 
proportion of motor-driven traffic, it is sometimes possible to pro- 
tect the surface with a thin bituminous coating which will resist 
the action of both the horse-drawn and motor-driven traffic, and thus 
prolong the life of the road surface. 

585. THE Bituminous Material. The bituminous material 
should be fluid at ordinary temperatures in order that it may be 
applied cold and spread uniformly. It should contain a small amount 
of volatile oils which will evaporate and leave a cementitious film 
on the surface. A light refined tar which is fluid at ordinary tem- 
peratures (§ 571-72) is generally used. An asphaltic oil containing 
from 40 to 50 per cent of asphalt gives fair results. Oils are cheap 
and readily appUed ; but are not entirely satisfactory for bituminous 
coatings for the following reasons: 1. Most petroleum products, even 
those having an asphaltic base, while in a fluid state act to a certain 
extent as a lubricant. 2. Both medium and heavy asphaltic oils 
require considerable time to set up; and therefore, if the road is 
opened to travel before the oil has set, more or less movement of the 
coating will take place, and it will become wavy and full of bumps. 

The amount of tar or asphaltic oil should rarely exceed 0.2 of a 
gallon per square yard, and an excessive amount is specially to be 
avoided. 

586. The field for this form of surface is comparatively limited, 
and the effect of such a coating is only temporary; but this treatment 
is often a valuable means of carrying an old gravel or macadam road 
along until a better form of treatment can be given. It is more 
expensive and more permanent than an oil dust-layer (§ 329-31); 
but is cheaper and less permanent than a bituminous carpet (§ 588). 



298 BITUMINOUS SURFACES FOR ROA] 



Art. 2. Bituminous Carpet 

588. When the proportion of motor-driven traffic on a water- 
bound gravel or macadam road becomes considerable (see Table 26, 
page 177), it is more economical to protect the road surface with a 
bituminous carpet or blanket than continually to add screenings or 
gravel to supply binding material. In some cases the mat or carpet 
is added to prevent the road from being denuded of binder, and in 
other cases the carpet protects the stone itself from excessive wear, 
which is particularly important on a road built of soft hmestone. 
The bituminous carpet not only protects the road but eliminates 
practically all dust. 

In consideration of the large mileage of water-bound gravel and 
macadam roads built before the advent of the automobile, this 
method of treating such roads is very important. Under some con- 
ditions it is still economical to build new water-bound gravel and 
macadam roads, and cover them with a bituminous carpet; although 
owing to the difficulties of maintaining a bituminous carpet, it is 
usually wiser to build a bituminous-macadam or a bituminous- 
concrete road, 

589. THE Bituminous Material. Either refined tar (§ 568) 
or asphaltic oil (§ 551) may be used. The particular grade of tar 
or oil to be used depends upon the condition of the road and the 
amount and character of the travel. If the road has begun to ravel 
and most of the stones have been swept bare of binding material, a 
refined tar Hke that in § 571, or a heavy oil hke that in § 559 should 
be used. If some bonding material remains on the road surface and 
the large stones are not entirely exposed, a medium oil like that in 
§ 558 would be better. If the surface is tightly bound and hard to 
sweep free from dust and fine material, a tar product like that of 
§ 570 or a light oil like that of § 557 should be selected. 

690. Cleaning Road Surface. The road should be swept 

with a revolving power-broom and then with a hand-broom until 
the surface is entirely free from dust and fine particles. The bitumi- 
nous material adheres better if the road is sprinkled before treatment, 
but it should be allowed to dry before the bituminous material is 
applied. Unquestionably water on the road when the bituminous 
material is applied is harmful ; but the sprinkling washes off the dust 
and therefore is beneficial, provided the road is dry when the bitumi- 
nous material is applied. 



ART. 



2] 



BITUMINOUS CARPET 



299 



Fig. 94 shows the method of cleaning an old macadam road pre- 
paratory to applying the bituminous surface. 




Fig. 94. — Sweeping an Old Macadam Road before Applying the Bituminous Surface. 



691. Applying Bituminous Material. The binder may be 
applied either by hand or by machine. In the hand method, ordi- 
nary garden watering pots or special pouring cans are used, being filled 
from a large supply tank that is driven along beside the work. It is 
very difficult to apply the bituminous material evenly with a hand 
pouring car : and it is necessary immediately to follow the appHca- 
tion with a brush broom and sweep the surplus oil ahead. This 
method of applying the material is very slow and expensive, and is 
now seldom used except for small jobs and for patch work. 

There are many diffe?'ent types of machines for distributing the 
bituminous material, but in outward appearance they do not differ 
greatly from the oil distributor shown in Fig. 39 and 40, page 137. 

There are a number of hand-drawn cart gravity-distributors. 
Some horse-drawn distributors have gravity feed ; but the mechanical 
feed or pressure distributor is the more common, since it secures 
a more uniform distribution and permits more accurate regulation of 
the amount applied. Some of the distributors have their own 
heating device; but some are made for spreading cold oil, or depend 
upon an auxiliary heater. Some distributors deliver the bituminous 
material in small streams, and others in a fan-like sheet, while 
still others deliver it in a fine spray. It is claimed that the spray 
applies the material more uniformly, and that it strikes the surface 
of the road with enough force to penetrate all interstices and to blow 



300 



BITUMINOUS SURFACES FOR ROADS 



[chap. IX 



away all dust, and thus secures a good union with the stone of the 
road. 

Fig. 95 shows a distributing tank which is drawn with horses or 
behind a road roller. The special features of this distributor are: 
(1) the bituminous material is heated by steam from a road 
roller, and hence can not be burned; (2) the material is dis- 
charged by air pressure in the tank, and hence there are no pumps 
to become clogged; and (3) the first cost of the machine is low. 




Fig. 95. — Horse-drawn Pressttre Distributor. 



The same features are embodied in a self-contained automobile- 
truck distributor, which permits work at a greater distance from the 
central heating plant. 

Fig. 96 shows a motor-driven distributor. The distributing 
head is in three sections, either outside one of which may be 
turned up and put out of use. With both arms in use the total 
spread is 16 feet. Fig. 97 shows a spray in use making a patch. 
Views 1 and 5, Fig. 100, page 311, show a distributor spraying 
tar. 

592. The bituminous material may be delivered in railroad 
tank-cars or in barrels or metal drums. The first method is objection- 
able owing to the difficulty of having enough road surface ready 
to receive 8,000 to 10,000 gallons of tar. When the binder is delivered 
in barrels or drums, it is heated in a large kettle while the tank wagon 
is distributing a load. . . 



AET. 2] 



BiTtJMlNOtJS CAHPET 



301 



The heating should be done so as to heat evenly the entire mass, 
and the heating should be under positive control at all times. The 
tax should be heated to 93° C. (200° F.) and not above 121° C. 




Fig. 96. — Automobile Pressure Distributor. 



(250° F.). Any material heated beyond 121° C. should not be used. 
The distributing wagon should be supplied with one or more ther- 




FiG. 97. — Spraying Distributor Making a Patch. 

mometers to insure that the temperature of the tar when appHed is 
between the above limits. It is unwise to apply tar when the air 
or road is below 50° F. (10° C). 

593. The bituminous material is appHed at the rate of | to J 
gallon per square yard, in either one or two treatments. The carpet 
should be uniform in thickness, as otherwise the thin places will cut 



302 BITUMINOUS SURFACES FOR ROADS [cHAP. IX 

through, and the thick portions will bunch if soft, and crack if a 
hard uiaterial is used. The thinner the carpet that can carry the 
traffic the better. 

594. After the bituminous material has had a few hours to pene- 
trate the surface of the road, and after it has set up a httle, stone 
screenings or pea gravel is added at the rate of about 1 cubic yard 
to every 100 to 150 square yards of road surface. The size of the 
screenings or pea gravel should be such as will pass a |-inch screen 
and be caught on a :^-inch. The screenings should be from hard 
stone, and should be free from dust and fine material. The harder 
the stone the smaller may be the screenings. The screenings are 
spread by hand with shovels or with a revolving-disk mechanical 
spreader. After being spread, particularly if the work is done by 
hand, the screenings should be carefully broomed to secure a uniform 
thickness of not over f of an inch. 

The purpose of the screenings is to keep the bituminous material 
from being picked up on the wheels of vehicles, to make the surface 
less slippery, and to increase the wearing qualities of the road. 

595. After the screenings have been spread a few hours, it is 
advantageous to roll with a roller, preferably the tandem type, 
weighing between 8 and 15 tons; but the rolling is not vital. 

596. Value of Bituminous Carpets. Bituminous carpets on 
old water-bound macadam roads have been of great value in enabling 
such roads to carry a considerable amount of motor-driven traffic; 
and under some conditions it has been economical to build a new 
water-bound macadam road and cover it with a bituminous mat or 
carpet. Such a surface will usually last from 6 months to 2 years 
depending upon the amount and kind of travel. Bituminous sur- 
faces have not been as successful on gravel as on macadam, perhaps 
because the former are more difficult to clean; but with care a fair 
degree of success can be insured on gravel. 

597. Many attempts have been made to add a bituminous sur- 
face to a portland-cement concrete road, but with widely varying 
degrees of success. The concrete road ordinarily has a large amount 
of travel, and therefore usually has too many steel-tired horse-drawn 
vehicles for a bituminous carpet. It seems to be agreed that the 
following conditions are important: 1. The concrete itself must be 
good. 2. The concrete surface should be roughened by wear before 
the bituminous coating is apphed. 3. The surface of the concrete 
must be warm, dry, and clean when the bituminous material is 
applied. 4. A preliminary priming or paint coat of thin tar is 



ART. 2] BITUMINOUS CARPET 303 

advantageous. 5. Two thin coats of the carpet material are better 
than a single thick one. 6. A J-inch coating can not stand up under 
much horse-drawn traffic. If there is much horse-drawn traffic, it 
may be necessary to make the coating 1 to 1 J inches thick by applying 
several successive layers of tar and screenings. Possibly a bitumi- 
nous material will yet be made that will be more suitable for 
such use. 

The advantages of a bituminous surface on a concrete road are: 
1. It protects the concrete from wear. 2. It reduces the noise from 
the impact of horses' shoes and steel-tired wheels. 3. It removes the 
glare of the light-colored concrete. 4. It hides the black blotches 
made in ffiling the cracks and joints. 

598. Maintenance of Bitumen Carpets. The work of 
maintenance consists in patching the carpet where it wears through 
or peels up, and in removing bunches where the carpet has crawled. 
The patching is easily done by following the method employed in 
the original construction; but care should be taken that the spot 
to be covered is clean, dry and warm. 

It is not easy to remove the bunches. If the surface is soft, a 
scraping grader (§ 155) will sometimes sm.ooth the surface without 
peeling up the carpet; but the work must be done during warm 
weather and immediately after a rain. The bunches may be re- 
moved by hand with a shovel that is kept hot while in use; but the 
shovel will not last long. A sharp chisel-like cutting tool if made of 
heavy metal will stand heating better than a shovel, and will remove 
the bunches. The bunch can be softened by building a small fire of 
twigs over it, or by pouring kerosene over it; but this practice is 
likely to ruin the material for some distance around the bunch. 
There are surface heaters, i. e., a hood having a gasoline flame under 
it, which are used for removing sheet asphalt (Fig. 161, page 451), 
which can be employed for removing these bunches; but the process 
is slow and expensive, and the flame is likely to damage the material 
which is not removed. 

599. COST OF Bituminous Carpet. Before the recent dis- 
turbance of prices by the Great European War, the cost of oils or 
tars for bituminous carpets varied according to the grade of the 
material from 4 to 16 cents per gallon, but usually from 6 to 8 cents. 
In some states the total cost of a bituminous carpet has been as low 
as 3 cents per square j^ard, while in others it has been as high as 15 
or 20 cents. 

Below are the details of the cost of applying a Hght bituminous 



304 BITUMINOUS SURFACES FOR ROADS [CHAP. IX 

carpet to a gravel road and to a water-bound macadam road by the 
Illinois Highway Department in 1915. 

600. Gravel Road. The cost at Cairo, Illinois, of applying 0.5 
gallon of cold oil (Aztec liquid asphalt) containing 60 to 65 per cent 
of asphalt, and 0.006 ton of torpedo gravel, stone chips, and sand 
per square yard, to a gravel road If miles long, the average haul 
being 0.5 mile and the rate of pay for laborers being 15 cents per 
hour and for teams 40 cents, was as follows : * 

Cost 

Items. Cts. per 

Sq. Yd. 

Oil, 8184 gallons at 4.7 cents f .o.b. siding 2 . 34 

Torpedo gravel at 59 cents per cubic yard, f.o.b. siding 0.24 

Heating and applying oil, demurrage, etc 0.32 

Hauling gravel 0.5 mile and spreading 0.31 

Sweeping and cleaning old road . 034 

Freight on equipment . 54 

Superintendence, engineering, and inspection 0.21 

Total, exclusive of depreciation, over-head expense, and profits 3.99 

601. Macadam Road. The cost of applying a bituminous carpet 
consisting of 0.33 gallon of Trinidad B asphalt and 0.016 ton of 
torpedo gravel per square yard, the average haul being 1^ miles and 
the pay of laborers being 25 cents per hour and of teams 50 cents, was 
as follows : t 

Cost 
Items. Cts. per 

Sq. Yd. 

Field superintendence . 35 

Bituminous material @ 7.7 cts. f.o.b. siding 2 . 39 

Torpedo sand @ 1.825 per ton f.o.b. siding and stone chips @ $.140 2 . 67 

Hauling gravel and chips, If miles . 84 

Spreading gravel and chips . 56 

Sweeping and cleaning old road . 05 

Heating and applying material, demurrage, etc 1 . 04 

Freight and equipment . 15 

Repairs to equipment . 07 

Incidental expense . 22 

Patching holes and repairing culverts . 27 

Total, exclusive of engineering, inspection and rent of equipment 8 . 61 

602. State Reports. The annual reports of many of the State 
Highway Departments give detailed data of the cost of bituminous 

* Illinois Highways, December, 1915, p. 168; or Engineering Record, Vol. 73 (1916), p. 806. 
t Illinois Highways, December, 1915, p. 171. 



I 



ART. 2] BITUMINOUS CARPET 305 

road surfaces. For example, the 1915 report of the New York 
Commissioner of Highways, pages 177-94, shows the kind and quan- 
tity of bituminous material used, its cost, the amount applied per 
square yard, the area covered, the cost of labor, and the total cost 
for each road in each county treated in that year— a total of 1800 
miles. 



CHAPTER X 

BITUMINOUS MACADAM AND BITUMINOUS CONCRETE 

ROADS 

604. A bituminous-macadam road consists of two or more courses 
of broken stone, the wearing course of which is bound with bituminous 
cement apphed on the surface. Formerly this form of construction 
was usually called bituminous macadam by the penetration method, 
but sometimes simply penetration macadam. 

A bituminous-concrete road consists of one or more courses of 
broken stone, the wearing course of which is bound with bitumi- 
nous cement mixed with the stone before it is placed. Formerly this 
type of construction was usually called bituminous macadam by the 
mixing method, but sometimes simply mixed macadam. 

Since in both of these types of construction the binder may be 
either tar or asphalt, it would be appropriate and more definite to 
use the specific terms asphalt macadam or concrete, and tar mac- 
adam or concrete; and further it would not be inappropriate to use 
the terms native-asphalt and residuum-asphalt macadam or concrete ; 
and likewise coke-oven tar macadam or concrete, and water-gas tar 
macadam or concrete. For a distinction between bituminous con- 
crete and asphalt concrete, see § 891. 

The present use of the terms bituminous macadam and bitumi- 
nous concrete is based upon the analogy between the method of 
construction of these roads and that of macadam and concrete, 
respectively. 

605. The two methods of road construction considered in this 
chapter have come rapidly into use since about 1910. 

Art. 1. Bituminous Macadam Roads 

606. The drainage and the preparation of the subgrade is sub- 
stantially the same as for the forms of roads already discussed. 

607. Foundation. The foundation is often an old gravel or 
macadam road, usually the latter; and sometimes, though less 

306 



ART. 1] BITUMINOUS MACADAM ROADS 307 

frequently, a new gravel or macadam road is constructed for the 
purpose; and occasionally a portland-cement concrete foundation 
is used. 

If the foundation is an old water-bound macadam road, the sur- 
face should be swept with a machine broom. All fine material 
that is caked upon the surface and is not removed with the machine 
broom should be loosened by hand, and then the surface should be 
swept perfectly clean with a hand broom. The coarse stone should 
be exposed, so the bituminous binder may adhere well. 

If the foundation is a new macadam road, it should be con- 
structed as described for water-bound macadam roads (Chapter VI). 
Under the same conditions, the total thickness of the road, including 
the bituminous wearing course, may be a Httle less than that of a 
water-bound macadam road, as the bituminous top will not wear as 
rapidly as the water-bound, since the former is usually built where 
motor-driven traffic predominates and rubber tires have but little 
effect upon the bituminous top. The first and second courses of stone 
are laid, rolled, filled, sprinkled, and again rolled as described for 
water-bound macadam, except that the second course is not flushed, 
i. e., is not filled so much as to form a film over the surface. It is 
essential that there shall be no voids in this course to absorb the 
bituminous binder. The stone should be clean and dry when the 
binder is applied. 

608. Width. For a discussion of matters relating to the width 
and position of the improved wheehvay, see § 95-97. 

609. Maximum Grade. For a discussion of maximum grades, 
see § 79-85; and for recommended values for the maximum grade, see 
Table 15, page 57. 

610. The Crown. The crown for bituminous macadam should 
be less than for water-bound, f of an inch to the foot being enough. 
See Table 16, page 66. 

611. Wearing Coat. The wearing coat consists of a layer of 
l|^-inch to 2:^-inch stone and two applications of asphaltic cement 
or refined tar, each of which is followed by a layer of |-inch to :J-inch 
screenings. If the stone is soft, the size of the screenings may be a 
little greater than stated above; and if hard, a little less. 

The layer of stone should be evenly spread to such a depth that 
after rolling it will have a thickness of 2^ inches, and should then be 
rolled dry until the fragments have become firmly keyed together so 
that the stones will not move ahead of the roller or so that they 
can not be moved by the thrust of a man's heel. If the foundation 



308 



BITUMINOUS MACADAM AND CONCRETE ROADS [CHAP. X 



is new macadam (§ 607), this course should be spread a^d rolled 
while the top course of the foundation is still moist and soft; but 
should not be rolled so much as to force the slush of the foundation 
more than half way up into the voids of the course being laid. Fig. 
98 shows the rolhng of the layer of stone of the wearing coat in 
progress. It is important that this course be not rolled so much as 
to prevent the penetration of the bituminous binder; and on the 
other hand; the course should not be so open as to require too much 




Fig. 98. Rolling of Latek of Stone for Wearing Coat. 

binder to fill the voids. If the stone is hard, it may be necessary 
after the rolling is partly completed, to fill the voids by applying a 
coat of gravel, see Fig. 99. 

612. Bituminous Binder. The bituminous binder may be 
either asphaltic cement or refined tar. The asphaltic cement should 
meet some one of the specifications in § 537-38; and the tar should 
meet one of two specifications in § 572-73. Owing to its greater 
cementing value asphalt is better for a road to be subjected to heavy 
horse-drawn loads than tar. 

The asphaltic cement when applied should have a temperature of 
135 to 177° C. (275 to 350° F.); and the tar of 93 to 121° C. (200 to 
250° F.). 

The amount of bituminous cement for the first application should 
be just sufficient to penetrate the third course and fill all of the voids; 
and usually this will require about 1 gallon per square yard per inch 



I 



ART. 1] 



BITUMINOUS MACADAM ROADS 



309 



of thickness of the upper course ; and for the second appHpation from 
■J to f gallons per square yard. An excess of binder is not only 
expensive, but causes the wearing course to creep and form waves. 

613. Applying the Binder. For small jobs or where it is difficult 
to operate tank wagons, the bituminous material is shipped in barrels 
or drums, heated in open kettles, and applied by hand from pouring 
cans. For the best results, the binder should be hauled in tank 
wagons provided with a heater, one or more thermometers, and a 




Fig. 99. Filling Layee of Stone with Geavel. 



pump for distributing the binder under pressure in the form of a 
spray. The tank wagon must have wheels with tires so wide as 
not to make an appreciable rut in the surface of the road. The 
spreading must be done so as to secure absolute uniformity. The 
area covered with a barrel- or a wagon-load should be measured, and 
the rate of appHcation computed. After the binder has been applied, 
the surface should be uniformly black, but the spaces between the 
stones should show. The temperature of the stone or the air should 
not be less than 50° F. (10° C.) during the application. 

After the first coat of binder is apphed, a layer of :J-inch to |-inch 
stone screenings, not over | of an inch thick, is spread over the sur- 
face; and then the road is rolled. If there is an excess of uncemented 
screenings after the rolling, they should be removed with a push 
broom, for an excess will cause the seal coat (the last coat of binder) 
through lack of adhesion to the first coat, to peel off. 



310 BITUMINOUS MACADAM AND CONCRETE ROADS [CHAP. X 

After applying and rolling the screenings, a seal coat of -g- to f 
gallons of binder per square yard is spread by the same means as for 
the first coat; and the utmost care should be taken to put on the 
material uniformly. 

Finally, the road receives a coat of screenings of hard screenings 
or pea gravel, not over | of an inch in thickness; and is again rolled. 
The roUing is continued until a smooth surface is produced. The 
road is now ready for travel. 

The eight views in Fig. 100 show the various steps in construct- 
ing the wearing cost of a bituminous macadam road. 

614. Another Type of Bituminous Macadam. The wear- 
ing course of the preceding type of bituminous macadam road could 
be appropriately described as a course of stone grouted with bitumi- 
nous cement. The Massachusetts Highway Commission and others 
sometimes use a mixture of tar and sand for the grout instead of a 
neat bituminous cement. It is claimed that the sand materially 
stiffens and strengthens the road crust and decreases the oxidation 
of the tar. 

Fig. 101, page 312, shows two views of the construction of a tar- 
sand macadam road built by the Massachusetts Highway Com- 
mission. 

615. Characteristics of bituminous Macadam. This form 

of construction is adapted to roads having a moderate amount of 
travel with not many heavy horse-drawn loads on narrow tires. It 
has a pleasing appearance, and is well adapted to both horse-drawn 
and motor-driven traffic. The surface seems to deteriorate more 
rapidly where considerable quantities of mud are tracked on it. In 
warm weather, particularly if an excess of binder was used, there is a 
tendency for the surface to creep and develop undulations. 

There have been a considerable number of failures of bituminous 
macadam roads, apparently because of the neglect to observe the 
proper methods of construction, — perhaps through lack of knowl- 
edge, since the type is comparatively new. 

616. COSTo This form of construction usually costs about 15 
to 20 cents per square yard more than good water-bound macadam 
(§ 388-93). There has not yet been sufficient experience to deter- 
mine the cost of maintenance or the ultimate Hfe of the bitimiinous 
layer. 

617. Maintenance. Bituminous macadam is pecuHarly resist- 
ant so long as it is intact; but when once broken, due to defective 
materials or workmanship, or to wear of travel, or to the opening of a 



ART. 1] 



BITUMINOUS MACADAM ROADS 



311 




1. Spraying Tar on Layer of Stone. 2. Spreading f-inch Stone on First Coat of Tar 




3. Sweeping Screenings to Secure Uniform 
Distribution. 



4. Rolling after Spreading Screenings. 




6. Spraying Seal Coat of .Tax. 



6. Putting Screenings on Seal Coat. 




7. Final Rolling of Road. 8. Finished Road. 

Fig. 100. — Constructing Wearing Coat op Tar-Macadam Road. 



312 



BITUMINOUS MACADAM AND CONCRETE ROADS [CHAP. X' 



trench, it disintegrates rapidly. Under these circumstances the 
defective portion should be cut out, the sides and bottom of the hole 
coated with bituminous cement, and the hole filled with stone and 
cement well mixed and solidly tamped into place. It is well to leave 




1. Roller, Tank Wagon and Mixer. 2. Pouring Tarvia-Sand Grout. 

Fig. 101. — Constructing Tar-sand Macadam Road. 

the patch a little high, so it will not be low when finally consolidated 
by travel. 

If the surface of the road becomes dry and lifeless, a new seal 
coat should be applied at once. This will usually occur with a tar 
binder in two or three years, depending upon the amount and char- 
acter of the travel; and with an asphalt binder, in three or four 
years. Applying a new seal coat is pecuharly a case in which a 
stitch in time saves nine. 



Art. 2. Bituminous Concrete Roads 

619. In the form of construction considered in this article, the 
wearing course consists of a layer of crushed stone bound together 
by either tar or asphalt. The stone and the binder are usually 
heated before being mixed, and are laid while hot. 

The distinction between bituminous concrete as considered in 
this article and asphaltic concrete as considered in connection with 
asphalt pavements (Art. 2, Chapter XVI), is that in the latter the 
binder is always asphalt, and the aggregate is accurately graded so 
as to secure a minimum of binder and also a maximum stability. 
One form of construction gradually shades into the other, and it is 
impossible to draw a definite line between them. In the accurate 
gradation of the aggregates asphalt concrete is closely related to sheet 
pavements, and hence the two are considered together in Chapter 
XVI. 



ART. 2] BITUMINOUS CONCRETE ROADS 313 

620. All that was said in § 114-28 concerning drainage, sub- 
grade, and crown applies also to bituminous concrete roads. 

621. The Aggregate. Gravel may be used, but only for light 
traffic. Broken stone is generally used because of the better bond 
thus secured. The broken stone should be hard and of compact 
texture and uniform grain, be free from adhering fine material, and 
preferably should have rough surfaces and sharp angles. 

Bituminous concrete is sometimes laid with crusher-run stone; 
but since the stone is not so uniform, the result is not so good as 
where graded stone is used. 

For the best results the aggregate should be carefully graded. 
" Practice has demonstrated that a mineral aggregate which will 
comply with the following sieve analysis, using screens having cir- 
cular openings, will produce satisfactory results: All the material 
shall pass a l^-inch screen; not more than 10 per cent nor less than 
1 per cent shall be retained on a 1-inch screen; and not more than 
10 per cent nor less than 3 per cent shall pass a ^inch screen."* 

For a more full discussion of the grading of the mineral aggregate 
for bituminous concrete, see Art. 2, Chapter XVI — ^Asphalt Pave- 
ments. 

622. The Binder. The bituminous cement used in the mixing 
may be either tar or asphalt cement ; but the seal coat should always 
be asphalt cement (§ 541). The tar should conform to the specifi- 
cations in § 574-75 ; and the asphalt cement should meet the require- 
ments stated in § 539-40. 

The quantity of bituminous cement to be used in the mix will 
depend on the gradation of the broken stone and the character of 
the bituminous cement, the climatic conditions, etc. For an aggre- 
gate graded as in the preceding section, the mixture should contain 
between 5 and 8 per cent by weight of bitumen. 

623. Mixing the Concrete. There are two types of mixing, 
cold and hot. 

624. Cold Mixing. This method is employed only with a special 
grade of tar, and the concrete is usually mixed by hand. This 
method is not very common, and great care is necessary in using it. 
The stone must be perfectly dry, the weather must not be too cool, 
and there should be a considerable period of warm weather imme- 
diately following the completion of the road. This form of con- 
struction is suitable for light traffic; but not for heavy traffic, either 
horse-drawn or motor-driven. 

* Report of Committee of Amer. Soc. of Civil Engineers, Proc. Vol. 42 (1916), p. 1626. 



314 BITUMINOUS MACADAM AND CONCRETE ROADS [CHAP. X 

625. Hot Mixing. Usually the stone and binder are heated 
separately and then mixed in a machine mixer. 

Bituminous concrete can be mixed in an ordinary hydraulic- 
cement concrete mixer; but mixers specially designed for mixing it 
are much more satisfactory. There are various such mixers on the 
market. Some mixers are heated internally by an open flame, and 
others externally by a flame or steam. On account of the danger of 
burning the cement, the flame in the mixing chamber should not 
be used, except perhaps on small jobs and in repair work; and even 
then the flame should never be allowed in the mixer after the 
bituminous material has been added. 

The heating device should be easily regulated, so that there 
will be no danger of burning the binder. The most common cause 
of failure in bituminous concrete roads is the burning of the binder. 
A burned batch will not usually show when laid, but after a few 
months will reveal itself. 

626. The bituminous cement, if asphalt, is usually heated to 
about 135° to 177° C. (275° to 350° F.); and if tar, from 93° to 
135° C. (200° to 275° F.). The stone for the asphalt mixture is 
heated to about 150° C. (302° F.), and that for the tar mixture to 
about 100° C. (212° F.). Any asphalt or tar that is heated more 
than stated above should not be used. No tar should be heated in a 
kettle containing any asphalt, and likewise no asphalt should be 
heated in a kettle containing any tar; and any mixtures resulting 
from this cause should be rejected. 

When discharged, mixtures of asphalt cement and broken stone 
should have a temperature of not less than 93° nor more than 149° C. 
(200-300° F.). When discharged, mixtures of refined tar and broken 
stone should have a temperature of not more than 121° C. nor less 
than 66° C. (250-150° F.). 

The mixer should be designed and operated so as to produce a 
thoroughly coated and uniform mixture without any segregation 
of the stone and the cement. 

Bituminous concrete should not be mixed or laid when the tem- 
perature of the air in the shade is less than 50° F. (10° C). 

627. Laying the Concrete. If not mixed upon the street, 
the concrete should be hauled in canvas-covered wagons or trucks; 
and should be delivered at a temperature of at least 66° C. (150° F.). 
The hot mixture should be dumped upon platforms, shoveled into 
place with hot shovels, immediately raked to a uniform thickness, 
and then thoroughly compacted by rolling. The roller should be of 



ART. 2] BITUMINOUS CONCRETE ROADS 315 

the self-propelled tandem type weighing from 10 to 12 tons, and 
giving a compression under the rear roll of 250 to 350 Jb. per 
linear inch. The rolling should continue until all roller marks dis- 
appear. 

After rolling, the wearing course should have a uniform thickness. 
The experience with this type of construction is somewhat limited, 
but apparently a thickness of IJ or 2 inches is sufficient to stand the 
heaviest mixed traffic; and apparently a greater . thickness is unwise, 
since it has a tendency to creep and form bunches. The surface 
should be free from depressions and irregularities exceeding f of an 
inch under a 4-foot straight edge laid longitudinally. 

628. Seal Coat. As soon as possible after the completion of 
the rolhng, and while the surface is dry and clean, a seal coat of hot 
asphalt cement should be applied with a hand-drawn distributor, 
and be spread with a squeegee. The asphalt cement should meet 
the requirements in § 541; and should be applied at a temperature 
of not less than 135° nor more than 177° C. (275-350° F.) at a rate 
of ^ to 1 gallon per square yard. 

As soon as possible after the application of the seal coat, and 
not more than 20 minutes thereafter, a thin uniform layer of stone 
chips (|- to i-inch or ^ to ^-inch) should be spread and thoroughly 
rolled with the tandem roller described in § 378. 

Fig. 102, page 316, shows six views of the construction of a bitu- 
minous concrete road built in Pennsylvania. The maximum size of 
the aggregate in this case was that passing a ^-inch mesh; and hence 
the concrete could be leveled off by striking with a template — see 
view 3. Views 5 and 6 are included partly to fill out the plate and 
partly to show the two forms of distributors. 

629. Maintenance. See § 617, page 310. 

630. Cost. Under similar conditions, the cost of this type 
of road is usually about 20 to 25 cents more than that of water- 
bound macadam (§ 388-93). 

631. Comparison of Bituminous Macadam and Bituminous 

Concrete. Bituminous macadam is the more common, there being 
seven or eight times as much in use as bituminous concrete. 

The advantages of bituminous macadam are: 1. It is compara- 
tively cheap. 2. It requires no expensive machinery. 3. It is 
easily and quickly laid. 4. The cost for labor is comparatively 
low. The disadvantages are: 1. Considerable care is required to 
prepare properly the upper course of the foundation to receive the 
bituminous macadam. 2. There is difficulty in securing a uniform 



316 



BITUMINOUS MACADAM AND CONCRETE ROADS [CHAP. X 



distribution of the binder through the wearing coat. 3. It is prac- 
tically necessary to use an excess binder, and hence the surface 
may creep under traffic. 4. The quahty of the binder must be sac- 




1. Loading End of Mixers. 



2. Discharging End of Mixers. 




3. Striking Tar-Concrete. 



4. Rolling Tar-Concrete. 




5. Applying Seal Coat. 6. Applying Seal Coat. 

Fig. 102. — Construction of Tar-Concrete Road 



rificed to the requirements of the method of its apphcation. 5. 
The method is not apphcable in cold or damp weather. 

632. The advantages of bituminous concrete are: 1. It permits a 
perfectly uniform distribution of the binder. 2. It permits the use 



ART. 2J BITUMINOUS CONCRETE ROADS 317 

of a suitable quality and quantity of binder. 3. It can be laid in 
comparatively cold weather. The disadvantages aje: 1. The cost of 
the labor is comparatively high. 2. It is slow in application. 3. A 
considerable quantity of expensive machinery is required. 4. The 
total cost is somewhat greater. 



PART II 

STREET PAVEMENTS 

633. Good pavements are necessary to the highest development 
of the commercial, sanitary and esthetic hfe of a city. The large 
proportion of people now dwelling in cities makes the subject of pave- 
ments an important one; and the fact that the urban population is 
increasing much more rapidly than the rural, and also the fact that 
the public is awakening to the necessity of amehorating the condi- 
tion of life in the city, will make pavements of increasing concern 
in the future. 



CHAPTER XI 

PAVEMENT ECONOMICS AND PAVEMENT 
ADMINISTRATION 

Art. 1. Pavement Economics 

634. BENEFITS OF PAVEMENTS. The effect of pavements upon 
city life is so important and so far reaching that no enumeration 
is likely to include all of the benefits; but nevertheless it will be 
of advantage, particularly in discussing the proper distribution of 
their cost, to enumerate some of the more important of the benefits 
resulting from the construction of pavements. Briefly the principal 
advantages are: 

1. Good pavements lessen the tractive power required, and 
decrease the cost of transportation. See § 4-9 for a discussion of the 
cost of transportation. 

2. Good pavements increase fire protection by facilitating the 
transportation of the fire apparatus. 

3. Pavements establish a permanent grade, which is an important 
matter when other improvements are to be made. 

318 



1 



ART. 1] PAVEMENT ECONOMICS 310 

4. Pavements improve the appearance of the street by giving a 
uniform surface instead of the irregular one of an unpaved street. 

5. Pavements increase cleanliness, since the pavement is less 
dusty in a dry time and less muddy in a wet time than an unpaved 
street, and since they are easily cleaned. 

6. Pavements increase healthfulness by removing holes filled 
with mud and filth. 

7. Pavements permit pleasure driving at all seasons, and facih- 
tate social intercourse. 

8. Pavements allow the use of bicycles, which furnish to many 
cheap transportation and healthful recreation. 

635. In discussions of this subject it is customary to include the 
enhanced value of the adjacent property as one of the advantages of 
a pavement; but the increase in the value of the property is simply a 
measure of the benefits enumerated above, and hence should not 
again be included. 

The first three benefits above may be regarded as financial 
advantages and the last four as sanitary and esthetic. It is im- 
possible to compute even approximately the financial, much less 
the sanitary and esthetic, value of good pavements; but it is safe 
to say that they are an absolute necessity to both the business 
and residency of the larger cities and also for business districts of 
the smaller cities, and that on residence streets of small cities good 
pavements add greatly to the health, comfort and pleasure of fife. 

636. Investment in Pavements. The table on page 320 
was compiled from statistics pubhshed by the U. S. Census 
Bureau, and shows the total areas and cost of the different kinds of 
pavements in 1909 in the 158 cities having a population of over 
30,000.* The areas are probably reasonably accurate, but the unit 
prices are only approximate owing to failures to state what was 
included in the cost, i. e., whether or not it included grading, foun- 
dation, curb, gutter, etc. 

From this table it appears that the pavements in these cities 
have cost $695,936,294; and as the total population is 25,603,949, 
the pavements have cost $27.10 per capita. The area of pavements 
per capita varies greatly in the different cities, being practically 
independent of the size and location of the city; but the average 
seems to agree fairly well with the area of pavements in a number of 
very much smaller cities investigated by the author. Therefore, it 



* General statistics of cities for 1S09, Bureau of Census, Washington, D. C, 1913. 



320 



PAVEMENT ECONOMICS AND ADMINISTRATION [cHAP. XI 



will be assumed that the above average is representative of the entire 
country. According to the U. S. Census Report there were 41,717,- 
853 people dwelling in cities of 8000 population or over in 1916. 
Therefore the investment in pavement in these cities amounts to 
$1,046,320,000. Measured by the money invested, street pave- 
ments, except steam railroads, are probably the most important of 
any single class of engineering construction. ^ 



Investment in Pavements 

^. .' Asphalt— sheet 83,227,011 S( 

>^ 1 block 5,418,666 

Bithulitic 4,000,872 

Brick 53,870,578 

Cobble stone ^ 9,083,397 

Concrete, portland-cement 445,478 

Gravel— water-bound 43,634,491 

bituminous bound 4,674,605 

Macadam — water-bound 107,998,789 

tar-bound 3,008,919 

portland-cement grouted. 303,069 

Stone block 51,414,901 

Wood block— creosoted 2,936,047 i 

untreated 10,724,370 ) 

Other kinds 4,367,708 



Total 385,409,889 



yd. at $2. 75 = 


$238,874,281 


2.75 = 


14,901,331 


2.25 = 


9,001,962 


2.25 = 


120,208,805 


0.80 = 


7,166,718 


1.20 = 


434,576 


0.20 = 


8,726,898 


0.40 = 


1,869,842 


0.75 = 


80,998,082 


1.00 = 


3,008,919 


1.00 = 


303,069 


3.50 = 


179,950,183 


3.00 = 


8,808,141 


2.00 = 


21,448,740 


.20 = 


873,541 


" = 


$675,936,294 



637. Data for the year 1899 similar to the above were presented 
in former editions of this treatise; and apparently from 1899 to 1909 
the area of pavements increased 38 per cent, and the cost 71 per cent. 
The increase in area is due to the increp.se of pavements in each city 
and to the increase in the number of cities from 129 to 158. The 
increased cost is due chiefly to the increase in the area of pavements, 
but partly to the increase in the quality of the pavements and partly 
to the increased cost of labor and materials. The quahty of pave- 
ments has increased greatly in the last few years. For example, 
formerly stone-block pavement consisted of roughly dressed blocks 
laid on a sand or gravel subgrade with wide joints filled with sand or 
pebbles ; while now most stone-block pavements consist of accurately 
dressed blocks laid on a concrete foundation with close joints filled 
with bituminous or hydraulic cement. A corresponding improve- 
ment has taken place in most other forms of pavements. However, 
the cost of pavements has not usually increased proportionally, 
owing to improvements in methods of doing the work. Some of 



ART. 2] PAVEMENT ADMINISTRATION 321 

these improvements are: The cutting of granite blocks largely by 
machinery instead of wholly by hand; the use of the 4-wheeled 
scraper and the steam shovel in preparing the subgrade; improve- 
ments in the methods of handling and delivering the sand and gravel 
for the foundation; the mixing of the concrete for foundations by 
machinery instead of by hand; improvements in the methods of 
handling the pavement materials, etc. 

638. According to Bulletin No. 100 of the 1890 census, the 
average annual expenditure for pavement construction and repairs 
in the cities of the United States having a population of 10,000 or 
over, was $1.72 per capita, being $1.54 in the cities having more than 
100,000 population and $2.04 in cities from 10,000 to 100,000. No 
later data seem to have been collected. If the same rate of expense 
obtained in 1909, the total annual expenditure for pavements in 
cities of 8,000 or more population was $85,104,420. In some smaller 
cities the average normal expenditure for pavements is four to five 
times the average just stated. 

The first cost of pavement and also the annual cost is of such 
magnitude that merely as a financial question, street pavements 
deserve careful attention and systematic study, 



Art. 2. Pavement Administration 

640. Importance of Problem. The importance of pave- 
ments as an element in municipal finance seems not to be fully appre- 
ciated, and this subject has not received from municipal engineers 
and city officials the attention and study its importance merits. 
Whether measured by their influence upon the commercial, sanitary 
or esthetic life of the city, or by the amount of money invested in 
them, street pavements belong in the first rank of importance in 
municipal affairs. 

641. Present Conditions. The following quotation* shows the 
surprising attitude of the pubhc and municipal officials toward this 
important subject. 

'' One would suppose that a subject of the magnitude and impor- 
tance of pavements would be a matter of the most critical investiga- 
tion and scientific research; but it is safe to say that in no other 
branch of civil engineering is there expended so large an amount of 



* John W. Alvord, C.E., in "The Street Paving Problem of Chicago." A Report to the 
Commercial Club of Chicago, 1904. 



322 PAVEMENT ECONOMICS AND ADMINISTRATION [CHAP. XI 

money in so unsystematic a manner, and generally with such unsat- 
isfactory results. 

*' Pavements are primarily designed to accommodate travel; 
but scarcely any one in this country thinks of investigating the 
travel of a city systematically and thoroughly before proceeding 
to lay pavements. 

''Pavements are financial investments; yet few city officials 
before proceeding to raise the necessary capital, undertake to com- 
pile data from which to compute the cost of maintenance and the 
length of life or depreciation. 

'' jtreet pav ements are by far the most expensive single improve- 
ment that the municipaUty undertakes; yet in hardly any of the 
cities of this country are there suitable laws, proper organization, or 
sufficient public spirit adequately to care forthe investment after it 
is once made. 

" The improvement of streets is a legitimate method of adorning 
our cities; yet no one thinks of consulting recognized authorities on 
good taste in such matters, except in boulevards and parks. 

" Pavements have been a necessity of civiHzation since Rome was 
mistress of the world; but cities are still experimenting with the sub- 
ject without general and well-defined pohcies. Community after 
community repeats the fundamental experinients, and copies without 
reflection or study what it sees being done elsewhere. 

'' The managers of the railways of the country know to a cent the 
cost and the comparative utility of every bolt and scrap of iron that 
enters into their road ; and they can tell to several places of decimals 
of a cent the cost of moving a ton of freight or the cost of transporting 
a passenger a single mile. But the city officials in this country that 
can make more than a rough guess of these matters in connection 
with the enormously greater travel of cities, can be counted on the 
fingers of one's two hands." 

642. Causes of Present Conditions. The present anomalous con- 
ditions are due to the following causes:* 

1. " The administration of American cities change every few 
years; and seldom do officers of the municipality have the ambition 
or opportunity to become thorough masters of the broader require- 
ments of the problems with which they are confronted. 

"2. In a republican state the tax-payer is expected to have 
a deciding vote in the expenditure of the public moneys, especially 

* Jolm W. Alvord, C. E., The Street Paving Problem of Chicago. A Report to the Com- 
mercial Club of Chicago, 1904, 



ART. 2] PAVEMENT ADMINISTRATION 323 

those raised by local taxation. As a result, advancement proceeds 
no faster than the education of the whole mass of tax-payers. 

" 3. Different kinds of street pavement rise or fall in public 
estimation with an undue amount of popular fluctuation. This is 
because there is no pavement that is perfect for all classes of con- 
ditions; and the pavement that comes the nearest to meeting one 
set of requirements may be the furthest away from another set of 
requirements. The public having selected a pavement, perhaps ill 
adapted to a particular environment, and finding it lacking in im- 
portant particulars, is apt to thoughtlessly, and perhaps pettishly, 
condemn it in toto when such a sweeping verdict is not warranted. 
Even city officials in charge of such matters do not always inves- 
tigate carefully enough the causes which make for failure, and 
allow personal impressions to take the place of carefully investigated 
facts. 

'' 4. The engineers of this country, up to within a few years, 
have not generally interested themselves in the subject of street 
paving, because they have not been given very good opportunity 
to properly study the question. Finding the tax-payer a self- 
appointed and sometimes exacting authority, they have been obliged 
more or less to abandon the field, so far as its broader questions are 
concerned, and accept his dictum. The speciaHst on street paving 
has been long recognized abroad as an important factor in municipal 
progress; and of recent years, he is beginning to appear in the United 
States. Seldom, however, does an average city call for his services; 
and almost never do municipalities appoint commissions of such 
men with ample funds to make an exhaustive study of the street- 
paving problem in its broader requirements. 

" 5. The natural distrust for municipal authorities is the normal 
condition of mind of the American tax-payer. This is the inevitable 
result of a system that generally produces mediocre results. And 
nowhere are mediocre results more apparent and unhappy than in 
the work of street improvements. As a result, the average city 
administration, however honest its intentions, feels that it is without 
moral support. It does not initiate broad policies, or spend pubhc 
moneys for investigation and research; but it gropes its way in the 
darkness of chance, and plays its cards like an opportunist, post- 
pones all possible trouble to its successors, and blames all deficiencies 
onto its predecessors, while ever pleading for revenue for new experi- 
ments. A distrustful pubfic generally refuses to cooperate in legis- 
lation tending to increase taxation for the future, until absolutely 



324 PAVEMENT ECONOMICS AND ADMINISTRATION [cHAP. XI 

assured of wisdom and economy in the present. The public is at 
times a harsh judge, and does not easily overlook glaring imperfec- 
tions or fully analyze deficient results. 

" 6. The usual method in this country of assessing the cost of 
improvements to the abutting property has tended to give undue 
prominence to the property owner, as the representative of the pubHc 
in deciding upon and paying for street paving. As a matter of fact, 
the abutting property owner is an agent. Whenever possible he passes 
on to the rest of the community, in the form of increased valuation 
and rental of his property, the cost he is assessed. Often he recoups 
himself for his outlay many times over; and yet ordinarily he regards 
himself as a public benefactor, and as such claims the right to outline 
street policies which usually lead to his own pecuniary advantage 
rather than to that of the public. 

*' 7. The method of assessing the first cost of pavements on the 
property owner, and then maintaining the pavement out of the public 
fund, has resulted in the majority of cases in there being little, if 
any, maintenance. No municipality has ever had an adequate 
' general fund.' The general fund is the common prey of all the 
more novel municipal projects and ambitions; and the common- 
place uses to which it might be put will always be unduly curtailed. 

*' 8. There is no general public appreciation of the vital necessity 
of maintaining pavements after they are once laid; and as a conse- 
quence there has been no cooperation on the part of the pubHc in 
framing legislation and raising revenues for this purpose. In this 
country, the practice has been generally to build pavements at high 
first cost, and allow them to wear out with a minimum of repair. 

"9. Finally, in this country the street-paving problem is every- 
where regarded as a local or neighborhood problem. The general 
public has not yet come to regard it as a national problem, or even 
entirely a municipal problem; and hence the lack of appreciation 
of the broader municipal requirements, and the insufficiency of study 
of its fundamental principles. To this cause may be assigned the 
chaotic condition of the art and incoherence of the data now existing 
and the absence of any general principles which should govern the 
subject as a whole." 

643. Remedy of Present Conditions. The present unfortunate 
conditions could be largely remedied by making the investigations 
and by carrying out the policies mentioned below. 

1. The first requirement for a comprehensive plan for street 
pavements should be a study of the traffic conditions of the entire 



ART. 2] PAVEMENT ADMINISTRATION 325 

city, which should include a census of the origin, amount, character, 
direction, and density (the amount per foot of width of street or 
pavement) of the travel on representative streets in all parts of the 
city.* Such a census should be repeated at regular intervals so that 
the growth and tendency of the traffic may be known with as much 
certainty as vital statistics or the census of population, since only by 
so doing can a basis be found for sound present pohcies or for fore- 
casting future necessities. It is not possible to formulate any 
scientific and adequate plan for street pavements without knowing 
the present and prospective use to be made of the pavements. Un- 
fortunately, but few such census data have been obtained for any 
American city — see § 34. 

2. The streets should be classified as to the amount and char- 
acter of the travel, the width of pavement, the depth of foundation, 
the kind of wearing surface, the amount necessary for maintenance, 
etc. The highway departments of the several states have recently 
quite generally classified the rural roads according to the amount of 
travel, and have specified certain types of road surfaces for the dif- 
ferent classes of roads — for example, see Table 26, page 177. 

3. Careful records should be kept of the cost of repairs on differ- 
ent kinds of pavements under different traffic conditions; and an 
inventory should be made at stated intervals to determine whether 
or not a particular pavement is gradually deteriorating, which would 
serve as a rough check upon the sufficiency of the annual repairs. 

4. Careful records should be kept of the cost of cleaning different 
kinds of pavements under different traffic conditions. The cost of 
cleaning is a part of the cost of maintenance; and unless the annual 
cost of maintenance is known, it is impossible to compare accurately 
the total cost of different kinds of pavements. 

5. Observations should be made to determine the tractive force 
required to draw loads over different types of pavements. There 
are tables of tractive resistance for different road and pavements 
surfaces, — for example, see Table 7, page 20; — but such data are 
quite general and do not represent with sufficient accuracy the pave- 
ments for a particular city which are built under certain specifications 
and of materials more or less local. The railways of this country 
spend large sums to determine the tractive resistance on tracks of 
different types and under different conditions; and the results of 
such observations are of great importance in maintaining an economic 

* For a discussion of travel census for rural roads, see § 29-33. 



326 PAVEMENT ECONOMICS AND ADMINISTRATION [CHAP. XI 

relation between the cost of the up-keep of the track and the cost of 
drawing trains over the track. Corresponding data for street pave- 
ments would be helpful in determining when the condition of any 
pavement renders it unfit for further profitable use. 

6. The public should be educated as to the financial, sanitary, and 
esthetic importance of street pavements; and also as to the fact that 
the construction and maintenance of pavements should be left entirely 
to those who have made a careful study of such work. 

7. The laws should vest the power to determine when a street 
should be paved and to select the kind of pavement in either an 
elective board of long tenure so that its members may have an oppor- 
tunity to acquire knowledge of paving materials and policies, or in a 
commission of real experts appointed for that purpose. 

644. Apportionment of the Cost. There is much discussion 
as to who in equity should bear the cost of the pavement. There 
are three distinct views. 

1. A few claim that as they own neither a horse nor a vehicle and 
do not use the^payement , the y shouki not be required to pay for it. 
Although a resident may not travel upon the pavement, it is used 
by those who serve him; and a pavement confers other benefits 
besides those relating to transportation. It is entirely impracticable 
to distribute the expense according to the use made of the pavement. 

2. Others claim that the pavement is for the benefit of the general 
j)ublic of the city at large, and hence the abutting property should 

pay no more than that in other parts of the city. This claim ignores 
the fact that the abutting property secures a distinct benefit for which 
it should be required to pay. Laying at least part of the cost upon 
the abutting property tends to discourage a demand for lavish 
expenditures for unnecessary improvements, that possibly might be 
insisted upon if the city contributed the entire cost. 

3. Many hold that the benefits accrue only to the abutting prop- 
erty, and that therefore the owner of the abutting property should 
bear the entire cost. This claim disregards the fact that the pave- 
ment is for the use of the general pubHc, and benefits all the people 
and all those having business interests in the city. An improvement 
in any part of the city is an indirect benefit to the city as a whole, _ 
In excuse of this method of payment, it is sometimes claimed that, 
although the pavement confers a general benefit, the inequality 
will be compensated when all the streets are paved. The answer 
is that all the streets may never be paved, and besides traffic natu- 
rally concentrates on certain lines and nearly ignores certain others, 



ART. 2] PAVEMENT ADMINISTRATION 327 

and therefore some pavements will require much more care and 
expense than others. Further, there should be no objection to letting 
every property holder pay a part of his ultimate share as the work 
progresses, instead of paying it in a lump sum when the street in 
front of his own property is paved. The second or third view or a 
combination of them usually obtains (§ 645). Table 36, page 328, 
shows the method of apportioning the expense in fifty American 
cities.* 

The practice is slightly different for the grading, the original 
paving, and the re-paving. All of the cost of grading in 54 per cent 
of these cities is paid by the abutting property, in 32 per cent all 
by the city, and in 14 per cent part by each in varying proportions. 
The cost of the original paving in 62 per cent of the cities is charged 
entirely to the private owner, in 22 per cent entirely to the city, and 
in 16 per cent it is divided between the two. The cost of re-paving 
in 42 per cent of the cities is paid wholly by the property, in 40 
per cent wholly from the general tax, and in 18 per cent it is divided 
between the two. In some cities a street in an addition or sub- 
division is not accepted by the municipal authorities until it has been 
graded, and hence it is done at the expense of the abutting property; 
but on the other hand, some cities are wilUng to bear a part of the 
cost of the street improvement, and therefore pay for the grading. 
Only one quarter of the above cities pay the major part of the cost 
of the original paving, while 40 per cent pay the major part of the 
cost of re-paving. It is the custom, where there is a car track on the 
street, to require the railroad to pave an 8-foot strip for each track, 
the remainder being divided between the abutting property and the 
city at large in the same proportion as on the streets where there is 
no track. In some cities intersecting streets are regarded as municipal 
property, and the cost of paving the intersection is assessed against 
the street, i. e., against the city; but in others the cost of paving the 
street intersections is included in the charge against the abutting 
property. In most cities lots owned by the municipality pay the 
same proportion of the cost of the street improvements as private 
property, although usually special authority is required thus to assess 
municipal property. 

Table 36 also shows that as a rule the eastern and southern 
cities pay a larger proportion of the cost of pavements than do the 
western. This difference in practice is probably due chiefly to the 

* From an article on Theory and Practice of Special Assessments by J. L. VanOrnum, in 
Trans. Amer. Soc. of Civil Engineers, Vol. 38, p. 336-422. 



328 



PAVEMENT ECONOMICS AND ADMINISTRATION [CHAP. XI 



TABLE 36 
Apportionment of Cost of Pavements in Fifty Cities 



Ref 
No 


Locality. 


Grading, 
Per Cent 
Paid by 


Original 
Paving, 
Per Cent 
Paid by 


Re-paving, 
Per Cent 
Paid by 




State. 


City. 


Prop- 
erty. 


City. 


Prop- 
erty. 


City. 


Prop- 
erty. 


City. 


1 






50 
100 
iOO 


50 

ioo 

100 
100 
100 

50 
100 

50 

' 'd ' 
100 
100 

■25' 

100 

ioo' 
100 
ioo' 

50 
100 

' d ' 

"2c' 
c 

100' 

166' 

c 
100 

50c 
100 

c 


50 
100 
100 

67 
a 

"ho 

67 
50 
100 
100 
100 
100 
100 
75 

lOO' 

ioo' 

100 
100 
100 
100 
100 

100" 

100 
100 
100 
100 
100 
100 
100 
98 
100 
100 
100 
100 
100 

ioo' 
ioo' 
166' 

100 


50 
"33 

ioo' 

100 
50 
33 
50 

' d ' 
c 

"25 
100 

ioo 

100 
100 

c 

c 

100 

' "d ' 

"2c' 
c 

lOO" 
100 

100 

c 
100 

c 


50 
100 

"h" 

'ho 

67 

50 

100 

100 

lOO' 

■75' 



160' 
100 
100 
100 
100 
100 

ioo' 
ioo' 

50 
100 

ioo 

100 
98 
100 
100 
100 

■'56' 

ioo' 
166' 
ioo' 


50 


2 


Arkansas 


Little Rock 




3 




100 


4 


Connecticut 

Dist. of Columbia . . . 


Hartford 


100 


5 








6 


W ashington 




100 


7 






100 


8 


Florida 


Jacksonville . ... 


50 


50 


9 


Georgia 


\tlanta 


33 


10 


Illinois 




50 
100 
100 


50 


11 


Peoria 




12 






d 


13 


Iowa 


Burlington 


100 


14 


Kansas 


Topeka 






15 






100 

75 


100 


16 


Louisiana 


New Orleans 


25 


17 




Portland 


100 


18 


Maryland 


Baltimore 


100 
100 


100 


19 


Massachusetts 


Lowell . 


100 


20 


Springfield 


100 


21 


Worcester 


100 
100 

lOO' 
100 


100 


22 


Detroit 




23 


Minnesota 


Minneapolis 

St. Paul 


c 


24 


Missouri 




25 


Kansas City. 




26 




St. Louis 




27 




50 




28 


New Hampshire 


Manchester 


100 


29 




100 
100 
100 
100 
100 
100 
100 
100 
98 
100 
100 
100 

ioo' 

100 




30 


New York 


Paterson 


100 


31 




d 


32 


Ohio 


Brooklyn 


50 


33 


Buffalo 




34 


New York 


100 


35 






36 


Syracuse 




37 


Cincinnati 


2c 


38 




Dayton 


c 


39 


Portland 




40 


Pennsylvania 

Rhode Island 

South Carolina 

South Dakota 

Tennessee 


Harrisburg 




41 
42 


Philadelphia 

Scranton 


100 
50 


43 




100 


44 




100 


45 


Sioux Falls 


100 


c 


46 


Nashville 


100 


47 


Utah 


Salt Lake 


50 


c 


48 


Virginia 


Richmond 


100 


49 


Washington 


Seattle 


100 
100 




50 


'Wisconsin 


Milwaukee 


100 











a. 1 sq. yd. for each front foot; dty remainder. 
h. 3i sq. ft. " " " " ; " 

c. City pays for street intersections. 

d. City does not pay for street intersections, 






V 



1 



ART. 2] PAVEMENT ADMINISTRATION 329 

limited revenues of new cities and to the many demands upon the 
general tax for the numerous and varied necessities of rapidly growing 
municipalities; consequently the cost of pavements, improvements 
having a definite local benefit, has been charged to the abutting prop- 
erty. It is equitable and just that the cost should be borne jointly 
by the private property and the city at large, since then the cost falls 
upon both interests which directly profit by the improvement, and 
neither receives a substantial benefit without sharing in its cost. 

Ordinarily the proportion of the expense to be borne by the 
municipality and by the private property is determined wholly by 
financial considerations or usage, and is made uniform over the 
entire city; while equity and justice demand that a distinction should 
be made depending upon the character of the traffic. The interests 
of the general public in a street vary greatly between a residence 
street, a business street, and a general thoroughfare. To pave the 
first the public should pay only a small share, say, 20 or 30 per cent; 
for the second, say, 40 or 50 per cent; and for the third 60 or 75 per 
cent. Some such variation in the proportion to be borne by the two 
interests finds further justification in the fact that if the street 
becomes a general thoroughfare, some of the benefits enumerated in 
§ 635 as accruing to the abutting property may be nullified by the 
noise and dirt. 

646. Special Assessments.* The proportion of the cost of 
a pavement paid by the private property is usually collected as 
a special assessment, which has been defined as ''a compulsory 
contribution paid once and for all to defray the cost of a special 
improvement to property, undertaken in the public interest, and 
levied by the government in proportion to the special benefits 
accruing to the property owner." Special assessments differ from 
taxes, both general and special, in that the former are based upon a 
direct and measurable benefit conferred upon the contributor, 
which is the measure of his liability to be taxed; while taxes are levied 
for the maintenance of the institutions and interests of the govern- 
ment, without reference to the particular benefits conferred, according 
to the ability of the contributor to pay. The construction of pave- 
ments to be paid for by special assessment must be done under the 
direction of the public officials. 



* For an interesting and instructive dscussion of the history and theory of special assess- 
ments, see Special Assessments by Victor Rosewater — Vol. 2, No. 3 of Studies in History 
Economics and Public Law. 152 p., 6 X9 inches, Columbia College, New York, 1893. See 
also the article referred to in the foot note on page 327. 



330 PAVEMENT ECONOMICS AND ADMINISTRATION [CHAP. XI 

In a general way it may be said that there are two distinct 
methods of apportioning the amount to be paid by the private 
property; viz.: (1) according to the frontage, and (2) according to 
the area. 

647. Frontage Rule. By far the more common method of appor- 
tioning the assessments is pro rata according to the frontage upon the 
improvement. This method is often designated as the front-foot 
rule. Of the forty-five cities in Table 36, page 328, which assess the 
private property for street improvements, thirty-eight or 84 per cent 
follow the frontage rule, three use a combination of frontage and 
area, one uses area alone, one value alone, and in two of the cities 
the method employed is left to the judgment of the assessing board. 

Ordinarily the frontage is an equitable basis upon which to 
distribute the cost; but under some circumstances a rigid appor- 
tionment according to frontage gives anomalous results. For 
example, if most of the lots have their shorter side on the improve- 
ment and one has its longer side thus placed, the frontage rule will 
give inequality — particularly if the latter lot is very narrow. This 
condition frequently occurs — for example where the most of the 
lots front upon the street to be paved, while some front upon an 
intersecting street. In this case, it is customary to extend the 
assessment to the middle of the block; that is, assess the lots between 
the pavement and the center of the block, in which case it becomes 
a difficult matter to determine the equitable portion for each of these 
lots. A rigid adherence to the frontage rule sometimes works 
injustice near the intersection of two streets cutting each other at an 
acute angle. However, no method can be devised that may not 
require modification to fit unusual conditions. 

648. Area Rule. In a few cities, 7 per cent of those in Table 36, 
page 328, the cost of street improvement is distributed in proportion 
to the area of the abutting lots ; but usually the area is used in com- 
bination with the frontage. Thus in Brooklyn, N. Y., 60 per cent 
of the cost is distributed in proportion to the frontage and 40 per cent 
according to the area. An amendment to the charter of St. Louis 
proposes to charge 25 per cent of the cost of the pavement according 
to the frontage and 75 per cent according to the area. The area rule 
finds its greatest justification on curved streets. 

649. Corner lots are usually the cause of irritation and objection 
under either the frontage or the area rule, and the method of assess- 
ing them differs materially in different cities. In some cases each 
margin isconsidered a front on its proper street, without any modi- 



ART. 2] PAVEMENT ADMINISTRATION 331 

ification in the rate of assessment; in a few cases under the area 
rule, an additional per cent is imposed upon the corner lot for the 
pavement of either street ; but usually the corner is assessed according 
to frontage at a less pro rata than the inside lots, since it may be 
assessed on both streets. 

650. Terms of Payment. There are various methods of pay- 
ing the assessment. 1. The entire amount may become a lien 
upon the property as soon as the work is completed, to be collected 
(a) by the contractor, or (b) by the city acting only as collecting 
agent for the contractor, or (c) by the city, which also becomes 
responsible to the contractor for the pajnnent of the money. 2. 
The amount may be divided into equal annual installments, usually 
five or ten, with interest on deferred payments, to be collected 
(a) by the contractor, or (6) by the city, the contractor receiving 
special paving-district bonds, or (c) by the city, the contractor 
receiving general city-bonds. 3. The city may raise a paving fund 
by general tax or by selling bonds, and pay for improvements as made 
independent of the collection of the special assessments. The second 
method is the more common. The first is objectionable because the 
amount becomes immediately due; and the third is objectionable on 
account of the difficulty of making the assessments and collections 
keep pace with each other, and also because of a tendency to produce 
extravagance. 

651. Legality of Levy. Special assessments can be levied only 
under explicit authority of the law. The different states have 
very complete and explicit statutes governing special assessments; 
and the courts always hold that any material departure from the 
prescribed procedure invalidates the assessment. 

652. Guaranteeing Pavements. It is a common custom 
to require the contractor to guarantee the pavement for a term 
of years, which guarantee is supported either by an indemnifying 
bond or by a portion of the cost of the pavement retained by the 
municipahty until the expiration of the specified period. In some 
cases the guarantee is an agreement that if time shall reveal that 
the materials or the method of construction are not according to 
the contract, the contractor shall make the defect good; but in 
other cases, the so-called guarantee is virtually a contract to main- 
tain the pavement for the specified period and to turn it over in 
good condition at the end of that time. 

Apparently the guarantee originated in this country with the 
introduction of sheet asphalt pavements. The material was new, 



332 PAVEMENT ECONOMICS AND ADMINISTRATION [CHAP. XI 

the method of laying it was untried, and hence no city would run 
the risk of paying for an unknown and uncertain pavement; con- 
sequently the contractor agreed to guarantee the pavement for a 
period of years. At present most cities continue to exact a guarantee 
for asphalt pavement, ranging from five to fifteen years, on the 
ground that the method of testing the material and the manner of 
laying it are too httle understood by engineers to insure good and 
durable work without a guarantee. At the beginning of the use of 
brick as a paving material a guarantee was sometimes demanded; 
but at present it is as a rule not required with this material. 

653. The requirement of a guarantee of the pavement is justi- 
fiable when the material to be used is new and there is httle or no 
opportunity for the engineering department to acquire the knowl- 
edge necessary for an effective inspection of the work; but as a 
rule a guarantee, particularly for a long time, is unwise for the 
following reasons: 1. The contractor has no control over the street 
after the pavement is completed; and it is difl&cult to discriminate 
between defects due to improper material and the effects of ordinary 
wear, which may differ materially on different streets. It is also 
difficult to discriminate between defective workmanship and damages 
due to causes for which the contractor is in nowise responsible, as, 
for example, fires, escape of illuminating gas, settlement of trenches 
made after the completion of the pavement, etc. 2. It is difficult 
to enforce the guarantee clause if, on the one hand, the engineering 
department inspects the material and accepts the workmanship; 
and, on the other hand, if a representative of the city does not inspect 
the work there is habihty that the streets may be needlessly obstructed 
and the pubUc greatly inconvenienced by a bungling experiment by 
the contractor. The difficulty of enforcing a guarantee is much less 
in a large city where there is more work to be had and where the 
contractor desires to protect his reputation with a view to securing 
contracts in the future, than in a small city having but little work; 
and the difficulty is still further increased if the law requires that the 
contract shall be let to the lowest responsible bidder — as is usually 
the case. 

The contractor objects to the guarantee, not without justice, 
on the following grounds: 1. The specifications are prepared by 
the engineering department of the city, and as the quahty of the 
material and the method of construction is prescribed by the city 
and subject to the approval of its representatives, the contractor 
should not be held responsible for the result. However, the suffi- 



ART. 2] PAVEMENT ADMINISTRATION 333 

cient answer to this objection is that the contractor accepts the 
specifications when he enters into contract, and is therefore right- 
fully bound by them. 2. The expense is needless and excessive, 
whether an indemnifying bond is required or a per cent of the con- 
tract price is retained, which expense in the long run adds to the 
cost of the pavement. It is more expensive to the contractor if 
the city retains a per cent of the contract price, since a portion of 
his capital is then tied up, which in turn drives out the small con- 
tractor, decreases competition, and tends to increase the cost of 
the pavement. On the other hand, the interests paying for the 
pavement are better protected if the city retains a per cent than if 
an indemnifying bond is accepted, since in the former case the city 
has the money in hand with which to make the needed repairs in 
case the contractor fails to do so; but the proper care of such de- 
ferred payments adds materially to the labor and responsibiUty of 
municipal administration. 

The contributing property holders and citizens favor the guar- 
antee as a defense against incompetent or dishonest city officials 
and employees. The guarantee is also sometimes defended on the 
ground that it is the cheapest method of securing good work, since 
it is impossible at reasonable cost for the engineering department 
to inspect all stages of the preparation of the material or to acquire 
the knowledge necessary for an effective supervision of the con- 
struction; but in general this claim is not true. It is neither credit- 
able to the engineering profession nor economical to the municipali- 
ties to leave all exact knowledge of paving matters in the hands of 
the paving contractors. 

654. The proper length of the guarantee period is a matter 
about which there is considerable difference of opinion. For asphalt 
pavement a guarantee for five years is quite common, although some- 
times a fifteen-year guarantee is required. With stone block, brick 
and most other forms of pavements nine months, or at most a year, 
is sufficient to reveal any serious defect of material or workmanship, 
and therefore a long guarantee is not necessary. 

655. Maintenance by Contract. As stated above it is common to 
require a so-called guarantee which is virtually a contract for main- 
tenance for the specified period. Maintenance by contract is justi- 
fiable if the engineering department of the city does not possess, 
or can not reasonably be expected to obtain, the information neces- 
sary in repairing the pavement; but as a rule maintenance by con- 
tract is undesirable, for four reasons: 1. The contractor has no con- 



334 PAVEMENT ECONOMICS AND ADMINISTRATION fcHAP. XI 



trol over the streets, and the repairs required are dependent upon the 
restrictions against opening the pavements and also upon the reg- 
ulations for keeping the streets clean. 2. It is difficult to specify 
beforehand the amount and the nature of the repairs that may be 
required by the ordinary use of the pavements, particularly as the 
opening of new streets or the paving of others may materially alter 
the amount or nature of the traffic on any particular pavement. 
3. It is impossible to determine accurately the condition of the pave- 
ment at the end of the contract period. 4. With a new and untried 
material it is impossible to determine what is a reasonable expense 
for maintenance. 

A contract for maintenance is sometimes defended by the prop- 
erty holders on the ground that thereby some one is secured who is 
admittedly responsible for the condition of the pavement and who 
is more amenable for neglect than are city officials. However, if 
the city officials can not be trusted to repair the pavements directly, 
it is doubtful whether they may reasonably be expected to super- 
vise the repairs to be made by the contractor. The choice between 
maintenance by contract and by municipal authorities directly 
will usually depend upon the local conditions. 

The pavements of Paris, France, were formerly maintained 
by contract, but are now maintained by the city directly. 

656. Tearing up Pavements. The most serious cause of 
the destruction of pavements is the frequency with which they are 
torn up for the introduction or repair of underground pipes, conduits, 
etc. No pavement has been introduced, and probably none ever 
will be, which is not seriously injured by being torn up. With care 
and intelligence a pavement may be replaced in nearly its former 
condition; but it almost never is so replaced, and under the condi- 
tions which such work is done, it is almost impossible to get it so 
replaced. The only remedy for the frequent disturbance of pave- 
ments is the construction of a subway in which to place pipes, 
wires, etc. ; but it is doubtful if any such remedy would be lasting for 
the streets are continually being put to new uses. Formerly it was 
thought sufficient to provide for water and gas pipes and sewers; 
while now conduits are required for telegraph, telephone, and electric 
light wires; and street-car tracks are constructed on the sm'face, 
above the surface, and below the surface; and in some cities space is 
required for pneumatic tubes, and pipes for distributing heat, com- 
pressed air, cold and hot water, etc. 

The only thing that can be done is to reduce the opening of the 



ART. 2J PAVEMENT ADMINISTRATION 335 

pavements absolutely to a minimum, and then to take the utmost 
care to see that as little damage as possible is done in making the 
opening and that the pavement is restored in the best way possi- 
ble. A few years ago in New York City a quarter of a mile of trench 
was opened for each mile of pavement, and in addition there was 
an opening for each 35 Unear feet of street. The year stated was about 
an average for those immediately before and after. In Chicago 
in 1902 200,000 square yards of pavements were taken up by pubhc 
service companies, which is equal to about 10 miles of pavement 36 
feet wide; or in other words, the equivalent of one sixth of all the 
new pavements laid in the city in that year was torn up by the public 
utilities corporations. This did not include the pavements taken 
up by the city itself to lay water pipes, sewers, etc. 

The amount of money spent in digging up the streets is a con- 
siderable item, not counting the interference with travel and busi- 
ness; but the expense, being distributed among various interests, 
is not usually sufficient to cause any one company to re-construct 
its system. It is probable that the interests of the pubhc are fre- 
quently sacrificed to the interests of the private companies using 
the streets — usually without paying for the privilege. 

Under the best municipal administrations of Europe neither 
corporations nor individuals are permitted to disturb the pave- 
ments. All removals and restorations are done by the city's own 
employees, upon the deposit, by the parties who require the streets 
to be opened, of a sufficient sum to cover the expense of each piece 
of paving done, at a fixed price per yard according to the kind of 
pavement. Moreover, interference with the pavements is of rare 
occurrence, for the companies having pipes underground are require 
thoroughly to examine and reinstate their mains and services con- 
currently with the paving of a street, due notice of the execution of 
which is given by the city. 

657. Nearly all cities have ordinances governing the opening of 
pavements, which differ greatly in character and severity; but gen- 
erally the result is unsatisfactory owing to the real difficulties of the 
case, or to inefficient administration, or to unexpected emergencies. 
There is also great variation as to the method of doing the back- 
filling, replacing the foundation, and re-laying the pavement, and 
also as to who shall do the work, — whether city departments, private 
parties, pubhc utihty compan}^, or contractor; and again none is 
satisfactory. This is a serious unsolved problem in American 
municipal administration. 



CHAPTER XII 



STREET DESIGN 



660. From the point of view of future needs — commercial, -sani^ 
tary, and esthetic, — it is unfortunate that cities grow up by successive 
additions under the stimulus of private greed and real estate spec- 
ulation, without any comprehensive or well considered street plan. 
In some instances — notably Paris, London, and Boston, — vast sums 
have been spent to correct what might have been prevented in the 
original plan of the streets.* In most cities transformation — slow 
and expensive, if it comes at all — is the only remedy; but a mended 
article is never as good as one originally well made.f 

Unfortunately there are few cities in this country having adequate 
regulations governing suburban development. Municipal authori- 
ties should regulate the street plan of subdivisions and additions so 
as to secure a harmonious whole, and particularly with a view of 
making the streets continuous and to afford suitable channels of 
communication. Where such regulations do not exist, streets will 
be laid out in such a way as best to develop the pp^rticular property, 
regardless of the interests of the public. Washington City, which 
has the best street plan of any American city, has been disfigured 
by ill-planned additions, although at present stringent rules govern 
the width and the arrangement of the streets of additions and sub- 
divisions. 

661. Street Plan. Since an engineer is occasionally called 
upon to plan a city, and often to lay out additions to cities and vil- 
lages, the various street plans for a city will be considered. In 
planning the streets of a city three objects should be kept in mind; 



* For example, Paris spent $14,000,000 in improving the Rue de Rivoli, and London $33,000,- 
000 on the Strand Improvement. 

t For an elaborate and abundantly illustrated treatise from the view point of an engineer, 
of many of the things considered in this chapter, see The Planning ofJthe Modern City, Nelson 
P. Lewis; John Wiley & Sons, New York, 1916. 

336 



STREET PLAN 337 



viz.: (1) the subdivision of the area in such a manner as to give 
the maximum efficiency for business or residence purposes; (2) 
sufficient accommodation for the pedestrian and vehicle travel 
on the streets; (3) good drainage; and (4) easy communicaition 
between the different parts of the city. 

662. Size of Lots. Owners in subdividing property are anxious 
to make as many lots as possible; and in some other respects small 
lots are to be preferred. It is desirable to make the lots of such a 
size that few of them will be subdivided, as clearness of identity in 
transferring or assessing the lot is maintained by always referring to 
the original number. A frontage of 25 feet seems the best. This 
width is suitable for business purposes, and for residence streets 
two or more lots will give proper grounds. Business lots are some- 
times made only 18 or 20 feet wide, but 25 feet is by far the more 
common. 

Lots are seldom less than 100, nor more than 180, feet deep; 
and usually vary from 100 to 150 feet. A lot more than 150 feet 
deep is objectionable, because of the temptation to build unsightly 
residences fronting on the alley and because of the usual indifference 
to keeping a deep lot in good sanitary condition. 

663. Size of Blocks. With a rectangular system of streets, 
the blocks are preferably long and narrow; since the distance re- 
quired between streets in one direction is only that necessary to 
give the proper depth of lots, while in the other direction the streets 
need be only close enough to provide convenient channels for the 
traffic. 

For convenience, especially in business districts, it is best to 
have an alley run lengthwise through the block. The alley varies 
from 10 to 30 feet, but is usually from 16 to 20 feet. 

The above depth of lot and width of alley makes the width of 
the block 220 to 330 feet. The length of the block will depend upon 
the requirements for traffic perpendicular to the principal streets. 
Sizes of blocks vary much in any particular city, and still more 
between different cities. The following are the dimensions of typical 
blocks in several cities: Boston, 220X400 feet, and 100X550 feet; 
New York, 200X900 feet, and 200X400 feet; Philadelphia, 400X550 
feet, and 500X800 feet; Washington, 400X600 feet, and 300X800 
feet; Montreal, 250X750 feet; Chicago, 300X350 feet, and 300X500 
feet. 

Fig. 103, page 338, illustrates the advantages to be derived from 
a careful study of the best size of blocks and of the most advan- 



338 



STREET DESIGN 



[chap, xii 



tageous arrangement of streets. The left-hand side of the diagram 
shows the typical arrangement of streets and blocks in the residence 
district of New York City, the shaded portions representing the 
usual buildings. The right-hand side shows a much superior arrange- 
ment.* The three center blocks of the present plan comprise an 
area of 720X800 feet, and contain 480,000 square feet of building 
area and 96,000 square feet of streets, and in the corresponding area 
of the proposed plan, there are 481,000 square feet of building area 






STREET "S 


^^^^^^^^^^^^^^ 


y//A COURT Y////. 


^^ 


'mmmmmm 




STRtElT ■§ 




Fig. 103. — Improved Arrangement of Streets and Blocks. 

and 94,200 square feet of streets; therefore the two plans give sub- 
stantially the same area for buildings and for streets. In the first 
case the length of streets is 1600 feet, in the second 1520 feet; 
therefore the two plans have practically equal Ught and air. The 
proposed arrangement is the better in the following particulars: 
1, number of corner sites; 2, accessibility of rear entrances for delivery 
of provisions, coal, etc., and the removal of garbage, ashes, etc., and 
in case of fire; 3, removal from the street of dangerous and cramped 



* Proposed by Mr. J. F. Harder, in Municipal Affairs, Vol. 2, p. 41-44. Reform Club, 
New York City, 1898. 



STREET PLAN 339 



cellar entrances; 4, removal from the main or primary streets of the 
loading and unloading of trucks; and 5, increased transportation 
facilities in a direction perpendicular to the length of the original 
blocks. 

664. Location of Streets. In planning a system of streets there 
are two objects that should be carefully considered, viz. : the drain- 
age and easy communication between the different sections of the 
city. Not infrequently these elements have been overlooked or 
neglected. The surface drainage, the sewerage and the travel must 
follow the general slope of the land; and therefore if there is much 
irregularity of contour in the site, a location of the streets with 
reference to the contours will afford at once the best drainage and 
the easiest communication between different parts of the city. If 
the site is nearly level, the relationship between the slope of the land 
and the direction of the streets is comparatively unimportant; but 
the arrangement of the street plan to afford the greatest facilities for 
communication between the different parts of the city is still an 
important matter. Therefore the conclusion is that on a site of 
irregular contour the streets should be located with reference chiefly 
to the topography, and on a level site primarily to secure the most 
direct and easiest intercommunication. 

665. Location with Reference to Topography. Unfortunately in 
this country our very desirable rectangular system of public land 
survey has frequently led to the adoption of a very undesirable rect- 
angular system of streets which, though convenient for dividing 
property into the greatest number of rectangular lots upon which 
can be built the greatest number of rectangular buildings, has little 
else to recommend it. Surface drainage sewerage and travel should 
follow the slope of the country, and any attempt to deviate from this 
becomes a serious question in the building of a city upon any but 
nearly level ground. The streets are of necessity the drainage lines 
of the city and should be placed in the natural valleys, and the failure 
so to locate the streets in many cities where the land is very irregular 
in contour has led to great expense in the construction of the streets 
and of a system of storm-water sewers. 

The upper half of Fig. 104, page 340, shows an actual case of a 
system of rectangular streets located without any reference to the 
topography; and the lower half of the same diagram shows a pro- 
posed arrangement * that would save much expense in grading the 

* By W. D. Elder in Proc. Michigan Engineering Society, 1898, p. 52. 



340 



STREET DESIGN 



[CHAP. XIl 



streets and at the same time give a quick entrance into the center 
of the city, and also give long easy grades from the heart of the 
city to the higher outlying district. 




inni 



1 1 I \7e/?fer(^ 



Fig. 104. — Locatiok of Streets with' Reference to Contottbs. 



STREET PLAN 341 



666. The original rectangular street system of San Francisco 
was laid out without much attention to the resulting street grades, 
some of which are 55 per cent. As rapidly as possible these excessive 
grades are being reduced. Recently $30,000 was spent to reduce the 
grade from 29 to 16 per cent through one block. The cost was 
something hke 15 per cent of the value of the abutting property. 
This extreme case involved several unique but expensive features.* 

667. Location with Reference to Directness of Communication. 
There are three distinct general plans for city streets with refer- 
ence to directness and ease of communication. 

668. One consists of a system of parallel streets crossing a similar 
system at right angles. This is often called the checker-board 
system, but more properly the rectangular system, since the blocks 
are not necessarily squares. This arrangement gives the maximum 
area for blocks, and also furnishes blocks of the best form for sub- 
division into lots. The rectangular system is the most common, 
and has its most marked exemplification in Philadelphia. 

669. A second arrangement of streets consists of the rectangular 
system with occasional diagonal streets along the Hnes of maximum 
travel. This system was employed by L 'Enfant in planning the city 
of Washington. Fig. 105, page 342, shows a portion of that city. To 
a limited degree, the same plan was adopted in laying out the city 
of Indianapolis, which has four broad diagonal avenues converging 
to a circular park in the center. These two are the only cities of 
any importance in which this system was adopted in advance of 
building. This system is usually, but somewhat improperly, called 
the diagonal system. 

The chief advantage of the diagonal street is the economy due 
to the saving of distance by traversing the hypothenuse instead of 
the two sides of a right triangle. In Rome, london, Paris, and 
in numerous other smaller places in Europe, whole districts have 
been razed to make way for new streets to serve as arteries for in- 
creased traffic. 

A second, and by no means an unimportant, advantage of the 
combination of the diagonal and the rectangular system is the open 
squares and spaces so grateful to the eye and of no little sanitary 
value in compactly built cities. New York City has recently been 
spending a milHon dollars a year to create such spaces by purchas- 
ing land and demolishing the buildings. 



* Engineering News, Vol. 75 (1916), p. 12-13. 



342 



STREET DESIGN 



[chap. XII 



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WIDTH OF STREETS 343 



Although the diagonal avenue occupies ground that might 
otherwise be used for building purposes, there is a compensating 
advantage in the greater length of street front obtained.* In many- 
cases the total cost of cutting diagonal streets through built-up 
districts has been paid by the increased value of the property on and 
near the street thus opened up. 

670. The third arrangement of city streets is the ring or concen- 
tric plan, which is very popular in Europe. The most noted example 
is Vienna with its Ring-strasse (ring street) within and its Gtirtel- 
strasse (girdle street) without. The former is 187 feet wide and 
encircles the public buildings and the leading houses of business and 
amusement. The enclosed network of streets intersect the Ring- 
strasse at forty points, and outward from it extend fifteen main 
radial avenues. 

671. Width of Streets. The width of city streets is important 
on account of its influence upon the ease with which traffic may be 
conducted and also because of its effect upon the health and com- 
fort of the people by determining the amount of light and air which 
may penetrate into thickly built-up districts. The streets of nearly 
all large cities are too narrow, being crowded and dark. A more 
liberal policy in planning streets would probably be of pecuniary 
advantage, since there is usually an enhanced financial value due 
to wide streets. A lot 100 feet deep on a street 80 feet wide is usually 
more valuable than a lot 110 feet deep on a street 60 feet wide; 
that is to say, within reasonable limits land is usually more val- 
uable in the street than on the rear of the lot. Wide streets are 
especially needed where they are bordered by high buildings or are 
to carry street-railway lines, f 

In order properly to accommodate the traffic in business dis- 
tricts of cities of considerable size, a street should have a width 
of 100 to 140 feet, the whole of it being used for roadway and side- 
walks; while residence streets in a city of considerable size, where 
the houses are set out to the property line and stand close together 
should have a width of 60 to 80 feet. Although it is advantageous 
to have a wide street, it is not necessary, nor even desirable that 
the whole width be paved; the central portion may be paved, a 



* For a discussion of this phase of the subject, see an article by L. M. Haupt in Jour. Franklin 
Inst., Vol. 103, p. 252. 

t For an elaborate and instructive article on this subject see a paper by John Nolen before 
the 1911 National Conference on City Planning, Engineering and Contracting, Vol. 35 (1911), 
p. 621-622. 



344 



STREET DESIGN 



CHAP. XII 



strip on either side being reserved for grass plats. The width of 
the pavement should be adjusted to the amount of travel, which 
varies greatly accordingly as the street is a business street, a thor- 
oughfare, or an unfrequented residence street. 

The width of the streets in different cities varies greatly. In 
the older places in New England and the Central States, many of 
the streets are only 30 to 40 feet wide; but in the West a street is 
seldom less than 60 to 66 feet wide. In both regions the princi- 
pal streets are often 80 to 100 feet wide, and in many of the larger 
cities the boulevards and great avenues are 150 to 180 feet. The 
main avenues in Washington are 160 feet wide, in New York 135, 
and in Boston, 180 feet. 

At present the regulations governing the width and the arrange- 
ments of additions and subdivisions of Washington, a city which 
has the best street plan of any in America (see § 669) are: '' No 
new street can be located less than 90 feet in width, and the lead- 
ing avenues must be at least 120 feet wide. Intermediate streets 
60 feet wide, called places, are allowed within blocks; but full- 
width streets must be located not more than 600 feet apart." 

672. Area of Streets. The proportion of the area of the 
city devoted to streets varies greatly, particularly between the 
older and the newer cities. The following is the per cent of street 
area in a few extreme cases of American cities : * 



Minimum Street Area 

1. Taunton, Mass 3.20 per cent 

2. Worcester, Mass 5.43 " " 

3. Binghamton, N.Y. . 7.55 " " 

4. PhHadelphia, Pa.. .. 8.42 " " 

5. Boston, Mass 8.76 " " 

6. Lowell, Mass 8.92 " " 

7. Fall River, Mass.... 9.17 " " 



Maximum Street Area 

Duluth, Minn 86 . 7 per cent 

Dallas, Tex 78 . 3 " 

Denver, Colo 73.9 " 

Indianapolis, Ind 56.4 " 

Washington, D. C 43.5 " 

Davenport, la 42 . 1 " 

Evansville, Ind 40.8 " 



The area devoted to streets and alleys in a few of the principal 
cities of the w^orld is as follows : 

Area of Streets and Alleys 

1. Washington 54 per cent 

2. Vienna 35 " 

3. New York City 35 " 

4. Philadelphia 29 •'' 

5. Boston 26 " 

6. Berlin 26 " 

7. Paris 25 " 



Census Bulletin No. 100— July 22, 1891,— p. IG. 



WIDTH OF PAVEMENTS 345 



673. Width of Pavements. It is wise to make the streets of 
residence districts of liberal width for sanitary and esthetic reasons; 
and also because the future of the street can not be certainly fore- 
seen, — the residence street may become a business street, or an 
unfrequented street a thoroughfare. However, it is not necessary 
that the whole width should be devoted to wheelways and side- 
walks, particularly in small cities. A grass plat between the side- 
walk and the pavement, in which shade trees are set (§ 696), adds 
to the beauty of the street and to the comfort of the residents by 
removing the houses farther from the noise and dust of the pave- 
ment. The grass plat or parking also affords an excellent place in 
which to place water and gas pipes, telephone and electric-light 
conduits, etc. In large cities where the street front is built up solid 
with houses of several stories, it may be necessary to dispense with 
the grass plat, and to devote the entire street to sidewalks and 
roadway. 

It is universally admitted that pavements are desirable; but 
often, owing to the unwillingness of at least some of the people to 
pay for them, it is difficult to secure them. Except for the cost, 
the wider the pavement the better; but length is more valuable than 
width. An excessive width is a needless expense, and delays or 
prevents the getting of any pavement at all; hence one help toward 
securing pavements is to make the pavement only wide enough to 
accommodate the traffic. Not infrequently the pavements of 
suburban and residence streets are needlessly wide. A narrow 
pavement not only costs less to construct, but also costs less to 
clean and maintain; while the cost of maintenance depends chiefly 
(or, with a pavement not subject to natural decay, wholly) upon 
the amount of traffic, and hence is nearly (or entirely) independent 
of the width. 

674. Without Car Track. A width of 18 feet affords sufficient 
room for a vehicle to pass when another is standing on each side 
of the pavement — a rare occurrence; — and therefore it appears 
that a pavement 18 feet wide is sufficient for the less frequented 
residence streets. The only objection to a very narrow pavement 
is the difficulty of turning a vehicle in such a street. The serious- 
ness of this objection depends upon the construction of the vehicle. 
Many dehvery wagons, express wagons, etc., may be turned on an 
18-foot pavement. If occasionally a vehicle is compelled to go to 
the corner turn, to or even to drive around the block, the incon- 
venience is not very serious, and is so infrequent as not to justify 



346 STREET DESIGN [CHAP. XII 

any considerable expense to prevent it. A width of 20 to 24 feet is 
probably sufficient for a majority of residence and suburban streets. 
When a residence street is an artery of travel, it may be necessary 
to make the pavement wider than stated above. In a number 
of cities, there has been a marked tendency in recent years to reduce 
the width of pavements on residence streets. 

Thirty feet affords sufficient room for two vehicles to pass each 
other where two others are standing at the curb; and therefore 
this width of pavement is ample for business streets in small places. 
On a narrow business street it may be necessary to curtail the width 
of the pavement to prevent the sidewalk space from being unduly 
encroached upon. 

In many of the cities the width of the pavement is uniformly 
a fractional part of the total width of the street, regardless of the 
needs of traffic. In many cities, both American and European, 
the pavement is three fifths or 60 per cent of the width of the street. 
In New York City and Brooklyn the rule seems to be to make the 
pavement half the width of the street. In Washington City there 
is no hard-and-fast rule, but the following is the usual relation: 
on streets 60 feet wide or less, the pavement is 25 feet or 40 per cent 
of the width of the street; on streets from 60 to 90 feet wide, the 
pavement is 25 to 35 feet, or 40 per cent; and for streets 130 to 160 
feet wide, the pavement is 40 to 50 feet, or 30 per cent. 

675. With Car Track. For a residence street containing a car 
track, the minimum width permissible is 28 feet, which will allow 
a car to pass with a vehicle on each side of the track. In Brooklyn 
a great many streets only 34 feet wide between curbs contain a 
double fine of street-car tracks, which leaves a space of only 9i 
feet between the track and the curb. This is astonishingly small, 
but seems to do fairly well 

On a business street containing a car track, it is wise to make 
the pavement wide enough to permit a vehicle to pass between 
the car and another vehicle standing at the curb. This will require 
about 48 feet. If the street is too narrow to permit this width 
of pavement and also the proper width of sidewalks, only one track 
should be allowed in the street; if a double track is necessary 
the cars should be required to make the return trip by another 
street. 

At Rochester, N. Y., the car tracks on residence streets are 
located on the parking at the side of the street. This is an unusual 
arrangement, but it possesses some advantages. 1. It separates 



STREET GRADES 347 



the vehicle and car traffic, and prevents mutual interference. 2. 
It permits a narrower pavement. 3. It prevents disturbance 
of the pavement to repair the car track. 4. It lessens the danger 
of a passenger's being struck by another car or a vehicle in leaving 
a car. The objection to this arrangement is that it interferes with 
the grade of the driveways to private grounds. 

676. Street Grades. The fixing of street grades is one of 
the most important functions of municipal engineering, since the 
grade system of the streets is the foundation of all municipal engi- 
neering matters. The grades should be estabhshed before the 
sewer system is planned; and if they are established before the 
property is improved the problem is comparatively simple, since 
they may be laid chiefly with reference to obtaining within proper 
hmits of cost desirable gradients for the street. But when build- 
ings have been erected, sidewalks constructed and trees planted, it is 
often extremely difficult to secure grades which will harmonize the 
various and confficting interests. 

677. Elements Governing Grades. The grades necessarily 
depend mainly upon the topography of the site; but in general the 
determination of the proper grade for a street requires the consid- 
eration of the following elements: (1) the drainage, (2) the cost 
of earthwork, (3) the accommodation of travel, (4) the effect 
upon the abutting property, and (5) the general appearance of the 
street. 

678. Drainage. The streets are the natural drainage channels 
of the city; the lots must drain into them, and the house must 
drain into the sewers placed in the streets. When no storm- water 
sewers are to be constructed, the grades become very important, 
since the streets must provide for the surface drainage of the city, 
and particular consideration must be given to relative grades and 
gutter capacities in order to prevent the excessive concentration 
of storm water at the lower levels and to provide for its proper 
distribution and disposal. 

679. Cost of Earthwork. Not infrequently the cost of making 
the excavations and embankments is given undue weight. The 
balancing of cuts and fills is often properly a controlling element 
in country road construction, but it should have relatively little 
weight in determining the grades of city streets. The expense 
for earthwork is incurred once for all, and a few hundred dollars 
more or less is usually unimportant in comparison with the expense 
of maintaining the street surface and the drainage system, and 



348 STREET DESIGN [CHAP XH 

the cost of conducting traffic over the grades, and also in com- 
parison with a better general appearance of the street. 

680. Accommodation of Travel. The question often is whether 
or not to secure ease of traction at the expense of increased cost of 
construction. The discussion in Chapter II, § 65-86, sheds a little 
light and only a Httle, as to the proper method of answering this 
question. Apparently engineers are incHned to overestimate the 
disadvantage to travel of a slight grade. Practical experience has 
demonstrated that there is not much difference in effect upon the 
cost of transportation between level roads and those having grades 
of 2 or 3 per cent unless such grades are very long or have an unusu- 
ally smooth surface. 

681. Effect upon Abutting Property. The private interests of 
the property holder should be carefully considered; although it 
is frequently impossible to establish proper grades without injury 
to the adjoining property. The general question is how far private 
interests should be sacrificed to the general good. It is better that 
the city or the other residents on the street should pay the owner 
damages than that lasting detriment should be done to the appear- 
ance of the street or to the traffic. 

682. General Appearance. Some attention should be paid to 
the appearance of a longitudinal view of the pavement. It is desir- 
able that the longitudinal grade be not changed so frequently as 
to give the street a wavy appearance. Further, the transverse 
grades at street intersections and on side hills should be so arranged 
as not to produce a confused appearance in looking along the street. 
The grades of the streets, both longitudinal and transverse, have a 
material effect upon the general appearance and beauty of the city. 

683. Maximum Grade. In a general way the principles gov- 
erning the determination of the permissible maximum grade of a 
city street are the same as for a country road, i. e., it is a question 
between the cost of operation on the one hand and the cost of con- 
struction and maintenance on the other, except that for a country 
road the cost of construction is chiefiy the cost of moving the earth, 
while for a city street the cost of construction should also include 
the effect upon abutting property of high embankments or deep 
excavations, and except further that usually in the city heavy 
loads can take a circuitous route and avoid the maximum grade 
entirely. In determining the maximum grade for a street, the 
fact should not be overlooked that the smoother the pavement the 
more serious is a steep grade. 



STREET GRADES 349 



684. In the Borough of Manhattan, New York City, are some 
business streets having grades as steep as 6 per cent, and a num- 
ber of residence streets have 10 per cent grades, and some have 
grades of 12, 15 and 18 per cent. Brooklyn, N. Y., has 4 per cent 
grades on business streets and 12 on residence ones. A number 
of cities have maximum grades on paved streets of 20 per cent — for 
example, Worcester, Mass.. Syracuse, N. Y., Borough of Rich- 
mond, New York City, and Pittsburg, Pa. Burlington, Iowa, has 
an 80-foot street with a 24 per cent grade up which is laid a zigzag 
brick pavement 18 feet wide having a maximum grade of 14| per 
cent with a minimum radius of the inside curb of 16 feet. San 
Francisco has some extremely steep street grades, for one example 
see § 666. 

For a discussion of the maximum grade for each kind of pave- 
ment, see the heading Maximimi Grades in the chapter treating that 
particular pavement. 

It is usually considered that a grade steeper than 15 per cent 
is impracticable and dangerous even for Hght traffic; and there- 
fore if this grade can not be obtained, the street should be divided 
into two parts separated by a terrace or stone wall, each portion 
being entered only at its intersection with the cross street — see Fig. 
118, page 358. A 10 per cent grade is usually considered prohibitive 
for heavy loads; and 5 or 6 per cent is considered the Hmit on busi- 
ness streets. 

685. The selection of the proper pavement for the maximum 
grade is a matter of great importance. For the recommendations 
of a committee of the American Society of Civil Engineers concerning 
maximum permissible grades, see Table 15, page 57. It is usually 
held that sheet asphalt should not be laid on grades steeper than 2 to 3 
per cent, although it has often been laid on 6 or 7 per cent grades, 
and in one instance on a 17 per cent grade (see § 887). Brick, or 
hard sandstone, or granite may be used upon the maximum grade. 
The sandstone and the granite blocks should be narrow and should 
be of a quahty that does not wear smooth. It has been recom- 
mended to chamfer the corners of rectangular stone or wood blocks 
when laid upon steep grades, to give the horses a good foot-hold; 
but it is at least doubtful whether the benefit of a good footing is 
not neutrahzed by the increased tractive resistance. The joints 
should be filled with tar or hydrauhc cement. 

686. Minimum Grade. The street surface should have enough 
longitudinal slope to drain its surface well With a smooth and 



350 



STREET DESIGN 



CHAP. XII 



impenetrable pavement no ruts will be formed, and hence the 
determination of the minimum permissible grade is mainly a 
question of the grade of the gutter. If the drainage is carried 
away by underground storm-water sewers, the street may be 
perfectly level longitudinally, since the necessary grade for the 
gutters may be obtained by making them deeper as they approach 
the inlet to the sewer. For a further discussion of this phase of the 
subject, see Grade of Gutter — § 711. 

If it is inexpedient to vary the depth of the gutter (§ 710) or to 
increase the grade by constructing additional inlets and catch basins, 
it is necessary to secure the proper slope for the gutter by inserting 
a summit in the street solely for drainage purposes — usually referred 
to as an accommodation summit. However, it is undesirable that 
there should be frequent changes in the grade, as they give the 
pavement an unpleasant wavy appearance when one looks along 
the street. 

687. Elevations at Street Intersections. One of the most impor- 
tant parts of the establishment of a system of street grades is the 

arrangement of the grades 



■Z(f- 



■• Y////A at street intersections. It 

is a common practice to 
estabHsh only the eleva- 
tion of the intersection of 
the center lines of the 
streets; but this often re- 
sults in much confusion in 
determining the elevation 
for the curb at the corner, 
particularly where the two 
streets have considerably 
different grades. For ex- 
ample, in Fig. 106, assum- 
ing (for the present at 
least) that the curb is to 
be at the same elevation 
as the center of the street opposite, the elevation of the corner of 
the curb, D, as computed from the grade of CB is 90.20 feet; 
while the elevation of the same point as computed from the grade 
of BA is 91.20 feet — a difference of 1.0 foot. To obviate this 
source of confusion, the elevation of each corner of the curb and 
also of the intersections of the center lines should be established. 



^ 



4 





<• ir^* 


^ 






\ 


D 


i 


i 


11 


I 




J 


J 




90^0 


Curb 







1^ 



.. < fZDotvn . 

Csnfer Line of ^3f reef 

Fig. 106. — ^Elevation of Curb at Corner. 



L 



c 



II 



STREET GRADES 



351 




/%D0M7 



Fig. 107. — ^Elevation at Corner of 
Property. 



A similar confusion occurs in attempting to compute the elevation 
of the corner of the property, from the grade of the corner of the 
curb. For example, in Fig. 107, assuming that the grade of the top 
of the curb is the same as that of the center of the street, and assum- 
ing that the sidewalk has a downward 
slope away from the property of 0.24 
inch per foot (2 per cent), and also 
assuming that the grade of the corner 
of the curb, D, has been established 
as 80.00, then the elevation of the 
corner of the property, G, as com- 
puted from the grade of the curb DE 
is 80.30 feet, while the elevation of 
the same point computed from the 
grade of the curb DF is 80.80 feet. 

Some engineers advocate estab- 
Hshing the elevation of the corner of 
the property and the determination of 

the grades of the curb and of the street therefrom; while others 
advocate establishing the elevation of the corner of the curb and from 
that determining the elevation of the corner of the property and also 
of the center of the street intersection. To be legal the elevation 
must be fixed by ordinance. The courts hold that the " elevation " 
is the top of the pavement in the center of the street; therefore 
it is necessary to establish by ordinance the elevation of the center 
of the street intersection. Further, to prevent misapprehension and 
error in computing the elevation of the corners of the curbs, and also 
to save the labor of computing them anew each time a lot is to be 
surveyed, it is wise to establish also the elevation of the corner of 
the curb. The ordinance should distinctly state the method 
to be employed in computing the auxiliary elevations of the 
sidewalk and of the corner of the property. Often the grades are 
established for only one street without due consideration of the 
intersecting street; and then when the second street is improved, 
the result is confusion, disputes, and sometimes suits for damages. 

688. When the rate of grade of both streets is small, it is desir- 
able that the entire street intersection from property line to prop- 
erty line should be level, a condition which permits the continuation 
of the section of each roadway until they intersect, makes the top 
of the curb at the four corners of the same elevation, and also allows 
the sidewalks at the corners to be level. That is to say, in Fig. 108, 



352 



STREET DESIGN 



[chap. XII 



the four points marked b and all the points marked a are in the 
same horizontal plane. Each street has its full crown on the hne 
bh, and consequently there is a shght rise from b to c. 

Where either or both streets have much inclination, it may not 
be wise to flatten out the intersection, and thereby increase the 
grade on the remainder of the street. Under these conditions, 
the best arrangement of the intersection is a matter requiring 
careful study and is one upon which there is much diversity of opin- 
ion. If steep grades are continued across intersections, they intro- 
duce side slopes in the streets thus crossed, which are troublesome 
and possibly dangerous — particularly to vehicles turning the upper 
corners. Such intersections are also objectionable on account of 

the difficulty , of properly caring 



J 

.^^^^i^^>^ 



X 



i 



b^' 



P 



Fig. 



I 

108. — Elevatioxs at Level Street 
Intersection. 



for the storm water. In resi- 
dence districts it is usual to make 
the intersection '^ level from curb 
to curb"; that is, in Fig. 108, the 
four points marked b are in the 
same horizontal plane. The 
level places serve as breathing 
places, and lessen the danger of 
colHsion at the intersection. 
However, if the street has a con- 
siderable grade, a level intersec- 
tion appears to have a decided 
pitch toward the hill, which 
gives the street an unpleasing 
appearance; and therefore under these conditions, it is better to 
apply, even in residence districts, the principle of the succeeding 
paragraph and give the intersection a moderate inclination down 
hill. If the intersection has only enough inclination to seem level, 
the general appearance of a series of such intersections is pleasing 
having the effect of a succession of terraces. 

The following rule * for adjusting the grades at street inter- 
sections is frequently employed and apparently is the most com- 
plete of any that has been proposed. '' In the business section all 
the street grades of 3 per cent or less should be continued unbroken 
over the intersection; and streets having a steeper grade than 3 



* Proposed by Messrs. Rudolf Hering and Andrew Rosewater for the streets of Duluth, 
Minn., in a report dated March 7, 1890. Engineering News, Vol. 25, p. 148-49; Engineering 
Record, Vol. 22, p. 53. 



STREET GRADES 



353 




Fig. 109. — Elevations at Inclined Street 
Intersection. 



per cent should have an intersection of 3 per cent between curb lines. 

The grade of the curb between the other curb line and the property 

Hne should in no case be greater than 8 per cent. The elevation at the 

corner of the property should be 

determined by adding to each of 

the elevations of the curb opposite 

the corner, the rise of the sidewalk 

and taking the mean." Fig. 109 

shows the elevations of a street 

intersection adjusted according to 

the above rules, assuming the 

transverse slope of the sidewalk to 

be 2 per cent (practically i inch 

per foot — the usual value) . 

The difficulty of adjusting ele- 
vations at an intersection is con- 
siderably increased if the two 
streets do not intersect at right 

angles. It is impossible to formulate any general rule, since each 
case must be decided according to the local conditions. Close 
observation and good judgment are required to secure a reasonably 
satisfactory adjustment. 

689, Notice that if either street has a grade and is carried past 
the intersection nominally unchanged, the area between the four 
curb corners and that immediately adjacent will be a warped surface. 

For example, in Fig. 110, if the street S 
has a descent as indicated and the street 
W is level, and the unchanged crowns of 
the street intersect at C, the area marked 
w must be raised to carry the upper side 
of the street W over the intersection, and 
the portions marked v must be raised to 
carry the street S over the lower side of 
the street W. If the grade of either street 
is small this adjustment can be made by 
" warping in " or ''boning in " the surface 
for a short distance. 

690. Vertical Curves at Grade Intersection. It is frequently 
claimed that the grade should be carried straight through from 
street intersection to street intersection, i. e., that the grade should 



1 



« 



IV 



'^r 



I 



M^ 



^ei/e/ 



J 



I 



Fig. 110. — A Warped Street 
Intersection. 



not be broken in the block. Apparently the reason for this practice 



354 STREET DESIGN [CHAP. XII 

is the claim that a break of grade between streets is unsightly. As 
usually put in, the angle of intersection is simply rounded off a 
httle by eye; and if the change of grade is considerable, the appear- 
ance is not good. A change of grade in the block is nowise different 
from a change at the street intersection, except that the former is 
a little more conspicuous. For both appearance and the comfort 
of the travel, wherever there is considerable change of grade, the 
two grade lines should be connected by a vertical curve; and if 
this is properly done, a break of grade in the block or elsewhere is 
unobjectionable. A vertical curve should be inserted at a change 
of grade either of the pavement or of the curb. 

By breaking grade in the block, it is possible to fit the grade 
line more closely to the natural surface, and thereby to decrease the 
cost of construction, to lessen the damage to abutting property, and 
to improve the general appearance of the street. 

691. A parabola is the best form for a vertical curve and is 
most easily put in. In Fig. Ill, AB and AC represent two grade 



Fig. 111. — Vektical Curve. 

lines meeting in the apex A, joined by the vertical parabola B C, 
which is tangent to the straight grade line at B and C. The curve 
may be located by measuring ordinates vertically below the points 
1, 2, 3, etc. The tangent distances A B and A C are equal. D E 
is equal to the rise in half the length of the curve, i. e., from B to 
A; and D C is equal to the fall in the second half, i. e., from A to C. 
If n represents the number of equidistant points to be established 
on the curve (including the second tangent point, C), then the 

ordinate at the first point = x = . The ordinate at 

any other point is equal to x times the square of the number of 
equal divisions between B and that point; that is, the ordinate 
from 2 is 4x, from 3 is 9x, from 4 is 16:c, etc. In actual work, the 



STREET GRADES 355 



grade elevation of the points 1, 2, 3, etc., are to be worked out in 
the usual manner; from these elevations subtract the ordinates as 
computed above, and the remainder is the grade elevation of the 
respective points on the parabola B C. The agreement of the eleva- 
tion of the last point on the curve, 6 in Fig. Ill, with the point C 
on the tangent, checks the work of computing the elevations. 

If the second tangent, A C, is level, D C in the above value 
for a; is ; and if the second tangent has an up grade, D C is minus, 
and the numerator = D E — D C. If the first tangent is level 
D E = 0; and if the first tangent has a down grade, D E is minus, 
and the numerator = D C — D E. The principles deduced for 
Fig. Ill are equally true, if that diagram be turned upside down. 

To secure the best results, there should be 15 feet of curve for 
each 1 per cent of change of grade, although 10 feet for each 1 per 
cent will give fair results. Long vertical curves make a graceful 
street. The effect of any proposed curve in lowering (or raising) 
the apex can be judged of beforehand by remembering that the 
distance from the apex A, Fig. Ill, to the curve is equal to half of 
the difference in elevation between A and the mean of the elevations 
of B and C. 

692. Crown of Pavement. The only reason for crowning a 
pavement, i. e., for making the center higher than the sides, is to 
afford surface drainage; and therefore the proper crown to be given 
to pavements will be considered under the head of Street Drainage 
— see Chapter XIII. 

To make intelUgible the discussion of the succeeding section, 
it is necessary to state here that in general the surface of the pave- 
ment consists either of two planes meeting at or near the center, or 
of a flat convex curve, usually the latter; and for present purposes 
it is sufficient to say that the average transverse slope is usually 
between 1 and 3 per cent (see § 720-24). The smoother the pave- 
ment and the better the construction, the less should be the crown. 

693. Cross Section of Side-hill Streets. The arrange- 
ment of the cross section of a street upon a side hill is a matter 
requiring good judgment, that needless damage may not be done to 
the abutting property or that the general appearance of the street 
may not be uselessly sacrificed. In solving this problem no fixed 
rules can be laid down; but each case must be treated by itself, 
taking into account the local conditions. Fig. 112 shows the normal 
arrangement for a residence street on level ground; both footways 
are at the same elevation, the slope of the parking is the same on 



356 STREET DESIGN [CHAP. XII 

the two sides, the tops of the curbs are at the same level, the gutters 
are of the same depth, and the surface of the street rises equally from 
each side to the center. The normal section for a business street 



^ — 



Fig. 112. — Cross Section of Street on Level Ground 

would be the same except that the sidewalk would occupy all of the 
space between the curb and the building line. On a side-hill street 
the above conditions can not always be realized; and various expe- 
dients must be resorted to, depending upon the difference in eleva- 
tion of the two sides of the street. The following are some of the 
common expedients. 

1. If the difference is not very great, the curbs may be set at 
the same level, and one sidewalk may be placed higher than the other, 
the grade of the parking being different on the two sides. On a 
business street, where there is no parking, the slope of the footway 
may be different on the two sides. With sidewalks consisting of 
stone slabs, cement, or asphalt, a slope of at least \ of an inch per 
foot (1 in 96) is required for drainage; and a slope of more than f 
of an inch per foot (1 in 32) is dangerous when covered with ice or 
snow. 

2. A slight difference of level may be overcome by raising the 
curb, i. e., by increasing the depth of the gutter, on the high side, 
and lowering the curb on the low side, the crown of the pavement 
remaining symmetrical about the longitudinal center hne. Fig. 113 




Fig. 113. — Cross Section of Side-hill Street. 

shows an actual section of a street arranged on this plan.* Except 
under extreme conditions, the curb should not show more than 10 
inches because of the difficulty of stepping to or from the pavement, 
nor less than three inches because of the danger of its being over- 
flowed when the gutter is full of melting snow. 

♦ Trans. Amer. Soc. of Civil Engineers, Vol. 42, p. 5, 



CROSS SECTION OF SIDE-HILL STREETS 357 

Sometimes a double curb is employed with a horizontal tread 
about 1 foot wide between the two risers. The combined con- 
crete curb and gutter (§ 737) lends itself most readily to this form 
of construction. Fig. 114 shows such an arrangement.* The objec- 

.o!, milH ^ /Poacftrau H fVa/k 



h 13" -»^ 20] -*(»-. 20" -4»"fc- ti -4 

Fig. 114. — Double Curb for Side-hill Street. 

tions to the double curb are: 1, its cost; 2, the difficulty of keeping 
the step neat and sanitary; and 3, it lessens the width available for 
roadway and sidewalk. In practice these objections have not proved 
to be serious. Instead of the double curb, it has been proposed to 
place the second step at the area line or propert}^ line, to which 
arrangement, particularly on a business street, the owner is liable to 
object. 

3. A slight difference may also be overcome by making the upper 
side of the pavement nearly level and giving the lower half the normal 
slope. 

4. The crown may be moved toward the high side of the street, 
the profile for each side being determined in the usual way; that is, 
the surface of tlie pavement may be two planes meeting at the 



p — ■> * — 'H fc I ^ g. v- tsj — 7'T^^ ___~J 

Fig. 115. — Cross Section of Street on a Side Hill. 

crown with the intersection rounded off a little, or it may be two 
arcs of a circle or a parabola tangent to a horizontal line at the 
high point (see § 717 and § 718). Fig. 115 is an actual example 
of this method of solution.* If the longitudinal grade is consid- 




FiG. iW — Cross Section of Street on a Side Hill. 



arable, as it usually is ilnder such circumstances, there is no objec- 
tion to the upper side of the street's being exactly level transversely. 
The extreme of this solution is to make the surface of the pave- 
ment a right line from the upper to the lower side — see Fig. 116. 

* Trans. Amer. Soc. of Civil Engineers, Vol. 42, p. 5. 



358 



STREET DESIGN 



[chap. XII 



This arrangement has been objected to on account of its throw- 
ing all of the drainage to one side of the street; but this is not a 
serious objection, particularly if there is a considerable longitudinal 
grade, as usually there is. 

5. Where there is a considerable difference of elevation on a 
residence street, it is sometimes wise to place the footway next 
to the curb, and to allow the slope of the parking to unite with that 
of the property — see Fig. 117. 




Fig. 117. — Cross Section of Side-hill Street. 

6. When any or all of the above solutions fail, it may be neces- 
sary to terrace the street and to construct an upper and a lower 
roadway as shown in Fig. 118. For an example of the application 
of this method of treatment and some other interesting features, 
see § 666. 

694. When the street contains one or more street-car tracks, 
the problem of arranging a cross section on the side of a hill is still 
more complicated. It is necessary that the two sides of a track 
shall be at least nearly on the same level; but it is not necessary 
that the two tracks shall be at the same elevation. A difference in 
elevation of f of an inch between rails of the same track and of 3 
inches between adjoining tracks is permissible. 




Fig. 118. — Cross Section of Side-hill Street. 



696. Street Trees. It is always desirable both for the shade 
and for the appearance to have residence streets hned with trees on 
each side. Although trees in the streets have an important sanitary 
and aesthetic value, opinions differ regarding the proper responsi- 
biUty for them. One view vests all right and title to the tree in the 
owner of the property before which it stands; and the other asserts 
that the trees belong to the city at large, and that the individual 



STREET TREES 359 



has no more right to the tree in front of his property than has any 
other citizen. In the first case, the planting of the tree, its kind, 
position, and care depend upon the public spirit of the property 
holder; and as a result the street presents a motley, straggling 
appearance often with no trees where they are most needed for the 
best general effect. Without some degree of public control, it is 
impossible even to approximate the best results of tree planting; 
but fortunately the number of cities in which the street trees are 
under the control of the municipal authorities is rapidly increasing. 

In planning a system of streets, the location of the trees should 
be definitely provided for. They should be located in the grass 
plats between the sidewalk and the edge of the pavement, and 
at a sufficient distance from both the sidewalk and the pavement 
that there will be no danger of the roots lifting either. The trees 
should be spaced in the row so as to permit each when fully grown 
to spread to its natural dimensions, which usually requires a space, 
center to center, of 25 to 40 feet. Not infrequently trees are planted 
much too close — particularly in the fertile and originally treeless 
prairies of the Mississippi Valley; — and crowd each other and pre- 
vent a symmetrical growth. In planting trees, it is well to alternate 
those of rapid growth with those which mature more slowly; and 
thien as the latter increase in size and demand more room, the former 
having served their temporary purpose, can be removed. Increased 
statehness, impressiveness, and charm is secured if the trees, at least 
the permanent ones, on any one thoroughfare are of one variety. 
Different streets can have different kinds of trees, since in nearly all 
cities there is a large number of suitable varieties available. 

697. In most states there are one or more cities that have ob- 
tained — either officially or by volunteer civic-improvement societies 
— valuable experience as to the varieties best suited to the environ- 
ment, from whom data can doubtless be obtained by those desiring 
information concerning the kind of trees to plant in the streets of 
any particular city. 

698. The following are the requirements for a street tree adopted 
by a commission of experts for Washington City.* "1: A some- 
what compact stateliness and symmetry of growth, as distinguished 
from a low spreading or pendant form, so that the stem may reach 
a sufficient height to allow free circulation of air below the branches. 
2. An ample supply of expansive foliage of bright early spring 

* Prpc, Amer, Sqc, Municipal Improvements, Vol. 5, p. 97. 



360 STREET DESIGN [cHAP. XII 



verdure, and rich in the variety of colors and tints assumed during 
autumn. 3. Healthiness, so far as being exempt from constitu- 
tional diseases, as well as from maladies frequently engendered by 
pecuharities of soil and atmosphere impurities. 4. Cleanhness, 
characterized by a persistency of fohage during the summer, freedom 
from falling flowers, and exemption from the attacks of noxious 
insects. 5. It should be easily transplanted, of moderately vigorous 
growth, and not incUned to throw up shoots from the root or lower 
portion of the stem. A tree of extremely rapid growth is generally 
short-lived. 6. The branches should be elastic rather than brittle, 
that they may withstand heavy storms; and lastly, there should be 
no offensive odor from foliage or flowers." 

Of course, no tree planted amid the artiflcial conditions found 
in a large city will fully meet such rigid requirements. In 1872, 
at the commencement of systematic tree planting, the above com- 
mission recommended the following list of trees. The Silver Maple 
(Acer dasycarpum), the American Linden (Tilia americana), the 
European Sycamore Maple (Acer pseudo-platanus) and the Amer- 
ican Elm (Ulmus americana) are thought to fill all the above require- 
ments when not subjected to the attacks of insects. The Tulip 
Tree (Liriodendron tulipfera). Sugar Maple (Acer saccharinum), 
Sweet Gum (Liquidamber styraciflua), and the Red Maple (Acer 
rubrum) are the most beautiful of trees, their only drawback being 
that of not growing freely after transplanting. The Norway Maple 
(Acer platanoides), the Negundo (Acer negundo), and the American 
Ash (Fraximus americana) are recommended for certain places. The 
Button-woods or Planes (Platanus occidentalis and Platanus orien- 
talis) are rapid growing, and for wide avenues are effective trees. 

As a result of twenty-five years' experience, the trees are ranked 
as follows: " Silver Maple, Norway Maple, and Eastern Plane side 
by side in the first rank; then the Ginkgo, and Western Plane; 
and last American Linden, Oak, and Sugar Maple." 



CHAPTER XIII 
STREET DRAINAGE 

701. The thorough drainage of a street involves four elements: 
(1) the surface drainage, (2) the gutters, (3) the catch basins, and 
(4) the underdrainage. They will be considered in the reverse order. 

702. Underdrainage. The underdrainage of a street is the 
first step toward paving it. Without thorough subdrainage a pave- 
ment is hkely to settle here and there, forming unsightly depressions 
on the surface, and possibly breaking through. The subsoil may be 
drained by one or more lines of porous tile as described in § 114-24; 
but as a rule the surface and underground waters are both collected 
in the same drain, and therefore it is advisable to lay a line of tile 
at each side of the street or to construct a larger conduit under the 
center of the street. Since the pavement is practically impervious 
to water, a third line of tile under the middle of the pavement is 
unnecessary, however wet and retentive the soil originally. 

If there is a grass plat between the pavement and sidewalk, as 
is usual on residence streets, the tile should be laid under the outer 
edge of the parking or grass plat; and if there is no parking, the tile 
should be laid under the gutter. The deeper the tile the better the 
drainage and the less the liability of its becoming choked with tree 
roots. The tile should not be too small since it is to carry both under- 
ground and surface water — the latter from a smooth and impervious 
pavement. 

The formula for size of tile for the drainage of earth roads 
(§ 119) is worthless for pavements, since in cities a large propor- 
tion of the rain falls upon impervious roofs, pavements, sidewalks, 
etc., and nearly all speedily reaches the storm- water sewers. This 
subject has been very carefully studied in connection with the 
design of sewers, and the reader is referred to treatises on that sub- 
ject, for further information concerning the size of drains or storm- 
water sewers required. 

.361 



362 STREET DRAINAGE [CHAP. XIII 

703. Catch Basins. The catch basin is a pit to receive the 
drainage from the surface of the street, in which is deposited the 
sand and other soHd matter, and from which the water is discharged 
into the sewer or storm- water drain. A catch basin should fulfill 
the following conditions: (1) The inlet should offer the least possible 
obstruction to travel, should have sufficient capacity to pass speedily 
all the water reaching it, and should not easily be choked by leaves, 
paper, straw, etc. (2) The capacity below the outlet should be 
sufficient to retain all sand and road detritus, and thus prevent it 
from reaching the sewer; and will depend upon the area drained and 
the intervals between cleanings. (3) The water level should be low 
enough to prevent freezing. (4) The construction should be such 
that the pit may be easily cleaned out. (5) The pipe connecting 
the basin with the sewer should have sufficient capacity, and should 
be so constructed as to be easily freed of any obstruction. (6) 
It is desirable that the outlet should be trapped so as to prevent 
floating debris from reaching the sewer. (7) If the catch basia 
discharges into a sewer which also carries house sewage, the end of 
the outlet pipe should be trapped to prevent the escape of air from 
the sewer to the street through the catch basin. 

704. The Construction. Catch basins are usually built of brick 
masonry, and plastered on the inside, at least up to the water fine. 
Fig. 119, page 363, the standard of Champaign, 111., is a good form. 
The opening of the inlet is protected by six half -inch iron rods. 
The several parts of the cast iron top are f and i inch thick; and 
the total weight of the castings is 162 pounds. The pit requires 
1,000 brick. The total cost of the catch basin when laid in 1 to 3 
cement mortar is $17.00 to $19.00, including castings, excavation, 
and the vitrified elbow. 

Fig. 120, page 364, shows the standard catch basin of Providence, 
R. I.* This form differs from that shown in Fig. 119 in the form 
of the inlet and of the trap for the outlet. The latter is made of 
iron cast in a single piece, and is somewhat complicated in form, but 
a careful study of the two views shown in Fig. 120 will make the 
construction reasonably clear. The seal in Fig. 120 is better than 
that in Fig. 119; but the latter is used only with storm-water sewers 
and for such use this trap is sufficient. Not infrequently, how- 
ever, the outlet of the catch basin is left untrapped; and some- 
times an inlet is connected to a sewer without the intervention 

* By courtesy of Otis F. Clapp, City Engineer 



CATCH BASINS 



363 



of either a catch basin or a trap. This practice is likely to clog the 
sewer. 

Fig. 121, page 365, is the standard for Milwaukee, Wis.* This 
diagram is presented to show (1) the form of the inlet, (2) the method 




Cro55 5ection 




a-o 
Plai? of Casting 

Fig. 119. — Champaign Catch Basin. 

of preventing floating debris from entering the outlet, and (3) the 
method of ventilating the sewer. 

Fig. 122, page 365, shows the standard form in St. Pancras 
Vestry, London, England, f 

In England many earthenware catch basins or '' gully pits " 



* By courtesy of C. J. Poetsch, City Engineer. 

t From a special report by William Nisbet Blair, Vestry Engineer. 



364 



STREET DRAINAGE 



[chap. XIII 



are used. Some of these forms are quite complicated. American 
engineers object to earthenware pits on account of (1) their Umited 




Plam' Without Manhole fiTAMC 
FiQ. 120, — Providekce Catch Basin, 



size, (2) their great cost, and (3) their habihty to be broken by the 
weight and jar of the street traffic. 

705. Location. The catch basin is usually placed near the curb 
with the cover in the sidewalk or the parking. It is objectionable 
to have the cover in the sidewalk, since (1) the cover itself is some- 
thing of an obstruction to travel and is dangerous when it wears 
smooth or is covered with snow, (2) the clearing of the pit seriously 
interferes with the convenient use of the footway, and (3) in empty- 
ing the pit the sludge is likely to be spilled on the footway, and at 
best the odor is offensive. In some cities these objections are elim- 
inated by placing the inlet at the curb line and conducting the drain- 
age to a catch basin near the center of the street, one basin serving 



i 



CATCH BASINS 



365 



for two or more inlets. Notice that the catch basin shov/n in Fig. 
122 cleans out in the gutter. 




%riP/onH 



Fig. 121. — Milwaukee Catch Basin. 

It is customary to place a catch basin at the corner of the curb. 
For additional objections to this location, see § 712. 

The number and capacity of catch basins will depend upon the 

Curb 



"^WafBrUne 




Outlet 



P/an 

Fig. 122. — London Catch Basin. 



area drained, the amount of rain, the grade of the gutter, etc. On 
streets having Hght or level longitudinal grades, catch basins may 
be constructed at intervals along the gutter as the circimistances 
require. 



366 STREET DRAINAGE [cHAP. XIII 

706. Form of Cover. When a catch basin or sewer manhole 
is located in a pavement, the shape and the surface of the cover 
require attention. The upper surface of the cover and also of its 
frame should be covered with projections to afford a good foothold 
and to prevent it from wearing sHppery. The best form for the 
frame depends upon the material of the pavement. For macadam 
and asphalt the round frame is best, since it offers least obstruction 
to travel; the next best form is a square frame set diagonally to the 
Hne of travel. For a pavement trade of bricks or stone blocks, the 
frame set with its sides parallel to the length of the street is beet, 
because the bricks or blocks can be most closely fitted against this 
form. In Europe and in many American cities, it is customary to 
use only a square form, and to set it diagonally in macadam and 
asphalt pavements, and square in stone block and brick. 

Often water-gate or stop-box covers are round in plan and have 
a convex surface, although the convex surface is very otjectionable. 
The better form is a cover round in plan with a flat recessed top 
set flush with the pavement. Preferably the portion below the 
ground should be provided with a cast screw for adjusting the height. 
This form may be had of dealers in street-drainage goods. 

707. The Inlet. In a general way, there are stone and cast-iron 
inlets. The former consist either of an opening between a stone 
cover and a stone floor, or a slot through the stone curb (see Fig. 120, 
page 364). This form is usually entirely open, but it is sometirres 
barred with one or two horizontal iron rods. 

There is a great variety of cast iron inlets on the market, which 
may be classified as being straight or curved, and also as having a 
vertical or a horizontal opening. Fig. 123 shows an unprotected 
straight vertical inlet. Sometimes the opening is protected by 





FiQ. 123. Fig. 124. 

one or more horizontal or vertical rods. The latter are the 
better, as they offer greater protection against the entrance of 
debris — particularly sticks and boards. Fig. 124 shows a. vertical 
front curved for a corner, having vertical bars. Fig. 125 and 126 
are two styles of a form having both a vertical and a horizontal 



CATCH BASINS 



367 



opening. Notice that Fig. 122, page 365, has only a horizontal open- 
ing. A horizontal opening is not so good as a vertical one, since the 
former is easily stopped by a few leaves, and the accumulation of 





Fig. 125. 



Fig. 126. 



water makes the stoppage more complete; while the barred vertical 
opening is less easily obstructed, and as the water rises it can pour 
over the obstruction already formed. 

708. Inlet without Catch Basin. It is sometimes desirable to 
connect two or more inlets to one catch basin — for example, see 
§ 713. There are various forms of such inlets on the market and 
many cities have their own special designs. Fig. 127, page 368, 
shows the form of inlet used in such a case at Omaha, Nebraska. 
The entrance A is reduced by cast ribs to three openings 6X9 
inches at the top and 4f X 2 inches openings at the bottom. The 
section B is rectangular in plan at both top and bottom. The 
section C is rectangular at the top and circular at the bottom, and 
fits into the hub of a vitrified elbow. Fig. 128, page 368, shows an- 
other form of curb inlet without catch basin. Fig. 129, page 369, 
shows a commercial form of inlet, which has an adjustable curb. 
It is made to fit various sizes of outlet pipe. 

709. Gutters. The Material. Ordinarily the surface of the 
pavement adjacent to the curb serves as a channel to convey the 
drainage to the nearest inlet, i. e., the gutter is formed of the same 
material as the pavement. With an asphalt or macadam pave- 
ment, it is customary to lay brick or stone blocks in the gutters — 
with asphalt to prevent its deterioration from being continually 
covered with mud and water, and with water-bound macadam to 
prevent flowing water from disintegrating it. 

A combined concrete curb and gutter (§ 737) is frequently used, 
particularly with asphalt, brick, or macadam on residence streets. 
A concrete gutter is objectionable on a macadamized street, on 
account of the crushed stone's wearing below the edge of the gutter, 



368 



STREET DRAINAGE 



[chap. XIII 



a condiaon which interferes with the drainage; but if the macadam 
surface is reasonably well cared for, this objection is not serious. A 




Fig. 127. — Omaha Inlet without Catch Basin. 

concrete gutter has been objected to for any pavement owing to 
the liabiUty of a rut to form along its outer edge. In practice neither 
of these objections has proved to be serious. A concrete gutter is 
more efficient and looks better than one of any other available 
material except asphalt (see last paragraph of § 710). 




Fig. 128. — Curb Inlet, Champaign, III. 



Usually the gutter is formed by continuing the ordinary slope 
of the pavement until it intersects the curb; but occasionally the 



« 



CATCH BASINS 



369 



outer edge of the pavement is given an upward inclination, thus form- 
ing a flat V-shaped channel a httle way from the curb. This con- 
struction makes an excellent channel for the water, but prevents 
the driving of a carriage close enough to the curb to allow people 
to step in or out easily. 

In some cases the curb is set and the gutter formed before the 
pavement is laid, in which case the curb and gutter are constructed 




FiQ. 129. — Commercial Inlet without Catch Basin. 



as they would have been if the street were to be paved, — the gutter 
being composed of stone blocks, bricks, or concrete (§ 709). Some- 
times a street is macadamized or graveled when it is not desired to 
incur the expense of setting a curb, in which case the gutter is built 
of cobble stones, or stone blocks, or bricks, in the form of a very flat 
V with the side next the property much the steeper. 

710. Depth. Where a curb is used, the gutter should not be so 
deep as to present a high step for pedestrians, nor so shallow as to 
be in danger of being overflowed. Not infrequently gutters are made 
needlessly deep. It is easier to keep a curb in line with a shallow gut- 
ter than a deep one. On streets having a considerable longitudinal 
grade the gutter can have a uniform depth, inlets being inserted 
to draw off the surplus water; but on streets having nearly level 
grades, the gutter must increase in depth as the inlet is approached. 
This can be done easily with a stone curb, but not so easily with a 
combination concrete curb and gutter (§ 737), since the latter is 
usually made in moulds having a uniform cross section; and there- 



370 STREET DRAINAGE [CHAP. XIII 

fore with a concrete curb and gutter, it may be necessary to put a 
summit in the pavement to secure proper drainage of the gutters. 
Except in extreme cases, the gutter should not be deeper than 9 inches 
nor shallower than 3 incbes; and ordinarily it should not be more 
than 8 nor less than 4 inches — usually it is 5 or 6 inches. 

It may be necessary to modify the preceding rules when one 
side of the street is higher than the other (see § 693). In localities 
where there is a good deal of snow, the gutter must be deeper than 
stated above, for shallow gutters readily become clogged with snow 
and slush. In some northern cities, the snow is habitually allowed 
to pack upon the surface of the street to a depth of 6 or more inches, 
in which places the depth of the curb must be extremely deep to 
prevent the melting snow and water from filling the gutter and 
flowing over the sidewalk into the basements. 

711. Grade. For most materials with which gutters are paved, 
it is improbable that the grade will be so steep as to do serious harm_. 
Crushed stone and gravel are exceptions to this rule, however, and 
these materials must not be laid on too steep a grade. They may be 
used on a 2 per cent grade provided the volume of water is not too 
great. 

The minimum grade permissible in the gutter will depend chiefly 
upon the material with which it is paved, but somewhat upon the 
cost of catch basins. Almost any grade can be obtained by estab- 
hshing catch basins close together and raising the gutter half way 
between them. In a number of cities the minimum grade of gutters 
paved with granite blocks, bricks, rectangular wood blocks, or mac- 
adam is 1 in 300 or 400. Except under very favorable circumstances, 
a slope of 1 in 200 (^ of 1 per cent) should be regarded as the minimum. 

Asphalt decays if continually wet, and therefore the condition 
governing the minimum permissible grade is different for that than 
or other materials. With a slope of less than 1 per cent, the gutter 
will not keep itself clean, consequently the asphalt will decay owing 
to the action of mud and water; and hence asphalt should not 
be laid in a gutter having a fall of less than 1 in 100. If this fall can 
not be obtained, a concrete gutter should be used, or the gutter 
should be paved with vitrified brick or carefully dressed granite 
blocks. 

712. Drainage at Street Intersection. In most cities it is cus- 
tomary to construct catch basins at the corner of the curb, using 
an inlet with a curved face. This practice is very objectionable. 

If the walk across the street is elevated above the pavement, it 



GUTTERS 



371 



is necessary either to carry the water under the walk in a pipe, or to 
stop the cross walk within a short distance of the curb to leave a 
channel for the water. The latter method is necessary where there 
is much water. Frequently this channel is left open at the top, and 
sometimes it is covered with a cast iron plate with one edge resting 
in a rabbet in the curb and the opposite one in a head stone or false 
curb set at the end of the cross walk. The covered gutter is much 
better than the open one, although the cast plates are frequently 
struck by wheels and broken, and often get displaced. This solution 
of the problem is further objectionable since a wheel in turning the 
corner must surmount the first raised cross walk, then descend to 
the bottom cf the gutter, and finally climb over the second cross walk. 
The face of the inlet usually has a depth of 8 to 12 inches below the 
top of the curb; and hence if the sidewalks are wide or the parking 
is narrow, the shock to a vehicle going around such a corner is con- 
siderable. 

If the cross walk is not elevated, the step from the curb to the 
bottom of the gutter is uncomfortably high, and besides pedestrians 
are compelled to cross the gutter where there is the most water. 

713. A much better arrangement than either of the above is 
to place an inlet at each side of the corner. Each inlet may have 



Curb. 



ft 



,—^Cafch Bas in 



/ 



.AS- 



Pbrfiing 



Wa/h 



its own catch basin, or the two 
may connect with a single pit 
by means of tile or vitrified pipe 
underground. Fig. 130, page 
374, shows such an arrange- 
ment. Instead of this plan, 
the two inlets at each of the 
four corners of the street in- 
tersection may be connected 
with a single catch basin 
placed in the middle of the 
intersection or in other suit- 
able location. The inlet not 
connected directly with a 
catch basin can be made by inserting the hub of a curved vitrified 
pipe in the bottom of a cast inlet-box (see Fig. 127, 128, and 129). 

The advantage of the method shown in Fig. 130 is that it allows 
the intersection to be paved almost level with the top of the curb, 
and hence there is no obstruction to either pedestrian or vehicular 
travel. The only objection to it is the expense for either the extra 



f 




Fig. 130. — Inlets at Street Corner. 



372 



STREET DRAINAGE 



:HAP. XIII 



catch basin or the extra inlet and connecting pipe, but the advan- 
tage is well worth this comparatively small cost. 

714. Where there are no storm-water sewers, the gutter is some- 
times carried across the street intersection. This is objectionable 
at any season, and particularly so when the gutter is filled with 
snow or ice. If the gutter is deep or the grade is steep, the water 
may be carried under the intersection by a shallow culvert with 
cast iron top, or better in a cast iron pipe; but if the gutter is shallow 
or the grade nearly level, the road surface should be raised a Httle 
to give room for a cast iron storm-water drain under the road- 
way. The elevated intersection may be a shght obstruction to 
travel, but it is preferable to two open gutters. 

715. Elevated Foot-way Crossing. To aid pedestrians in cross- 
ing the water in the gutter, it was formerly the practice to raise the 
pavement in the line of the crossing so that the surface of the foot-way 




PLAN 



I I I I I I I I I I I I I I i~rT 



SECTION A-B 



SECTION C-D 

(of the centre) 



a^HHHaHH^aHH 



SECTION E-F 

Fig. 131. — Elevated Brick Crossing. 



was level from the crown of the carriage-way pavement to the 
top of the curb, and leave a channel next to the curb which was 
either left open or bridged with a cast iron plate. Fig. 131 
shows the details of an elevated brick crossing. Notice that 
Fig. 131 has a Hmestone curb and a brick gutter. Fig. 132 and 133 
show the gutter at the end of an elevated brick crossing when a con- 



SURFACE DRAINAGE 



373 



Crete curb and gutter is employed. The chief difference between 
Fig. 132 and 133 is in the form of the false curb or head stone on the 
side of the gutter toward the center of the street. The difference 
in the merits of the two methods is mainly in the cost, Fig. 133 
usually being sHghtly the cheaper. In both cases there is a drop of 
1 inch in the width of the cast iron bridge plate. Of course, the 
crossing could be carried level from gutter to gutter, or more drop 
could be put into the gutter plate. 

It has always been recognized that as far as the use of the car- 
riage-way pavement is concerned, an elevated crossing is undesir- 



I5'xi' CI. Gutter RafB 



CI Gutter nik/fe 




Fig. 132. — Gutter for Elevated Brick 
Crossing with Concrete False Curb. 



Fig. 133. — Gutter for Elevated Brick 
Crossing with Limestone False Curb. 



able, particularly where the pavement is used by a large nimiber of 
vehicles or where there is considerable rapid travel; but since 
the introduction of the automobile, the elevated crossing is very 
undesirable. The elevated crossing is a serious obstruction also to 
vehicles rounding the corner; and besides the cast iron crossing 
plates are easily displaced and are frequently broken. The elevated 
crossing should not be used. 

716. Surface Drainage. The drainage of the surface of the 
pavement is provided for by making the center of the pavement 
higher than the sides. The principle governing the amount of crown 
for pavements is somewhat different from that of earth, gravel, or 
water-bound macadam roads. First, a hard, smooth and practically 
impervious pavement needs no crown for the drainage of the surface ; 
and on such a pavement, the only advantage of a transverse slope is to 
drain shallow depressions due to faulty construction, wear, or a set- 
tlement of the foundation, and to aid the rain in washing the pave- 
ments. Second, the surface of the pavement has no tendency to 
wash; and hence the crown need not be increased on a grade as in 



374 STREET DRAINAGE [CHAP. XIII 

the case of earth roads. The less the crown the better for travel, 
and the more uniformly will the travel be distributed over the pave- 
ment, although a shght crown is inappreciable in either of these 
respects. Therefore pavements require only crown enough to drain 
depressions of the surface due to faulty construction, to wear, or 
to settlement of the foundation; and the crown may decrease as 
the grade increases. 

717. Crown. There has been much discussion as to the best form 
of the surface of a pavement. Some claim that it should be a con- 
tinuous curve, while others contend that it should consist of two planes 
meeting in the center. The curved profile is defective in that it gives 
too little inclination near the middle, the result being that the pave- 
ment wears hollow in the center and permits water to stand there. 
To overcome this objection some engineers raise the center of the 
pavement ^ or f of an inch above the curved cross section. The 
objection to the two planes is that the sides wear hollow and hold 
water. An advantage of the curved profile is that the center of the 
street, which is the part especially devoted to travel, is nearly flat; 
while the sides, which have the greater inclination, are occupied by 
teams standing at the curb. Another advantage of the curved 
profile is that it gives a deeper gutter, which confines the storm 
water to a smaller portion of the street and reduces the interfer- 
ence with pedestrian travel. 

It is sometimes claimed that the curved form will support the 
greater load, because of its arch action; but the arch action of a 
pavement is entirely inappreciable, owing to the flatness of the arch, 
to the imperfect fit of the so-called arch stones, and to the insta- 
bility of the abutments or curbs. 

The surface is usually a continuous curve — generally a parabola. 

718. To Lay out a Parabolic Crown. In Fig. 134 the curved line 
C B represents the surface of the finished pavement. C is the center 
of the pavement; and C D = A B = the amount of the crown. 




Fig. 134. — Pababolic Crowned Pavement. 



To find the distance from the line A C down to the curved line C B, 
divide the half width of roadway, A C, into any number of equal 



SURFACE DRAINAGE 



375 



parts, say n, and designate the distance from the point \ on A C 
vertically down to 5 C by x; then by the principles of the parabola, 

A B 

X = — ^r-, and the distance from point 2 down to the road surface 

is 2^ X or 4 X, and the distance from 3 is 3^ a: or 9 x. In practice a 
string with knots in it to represent the points of division oi A C is 
stretched from the top of the curbs, and then the ordinates computed 
as above are measured with a pocket rule. 

719. When construction begins, it is wise to give the one in 
charge of the work a drawing somewhat like Fig. 135, showing 






4 


e 


1Z 


ie 


tz 


6 


4 


t 


i 


i 
_. * - 


1 




\ 


! 


-U 


IP — 








3ub-grxide 






— ' *l 






4 


6 


tz 


16 


tz 


5 


4- 


C 


L- 




t 


? 


t 


•^ 


^ 


•<; 


^ 






Concrvfe 







f— 



Bnc/r 

■ J^-o" 



tr- 



Fig. 135. — Method of Showing Crown of Pavement. 

the relation between the top of the curbs and the cross section of the 
subgrade, the top of the concrete, and the top of the finished pave- 
ment. Such a drawing prevents misunderstandings and disputes. 
Notice that the curves in Fig. 135 are not exact parabolas, the 
ordinates at 4 and 12 being ^ inch too long; but this is sufficiently 
exact, since it is not possible to secure mathematical precision in this 
class of work. 

720. Rules for Amount of Crown. The practice of different 
cities is not at all uniform as to the amount of crown. Numerous 
empirical formulas have been proposed for the crown of pavements; 
but there is not much harmony between them.* 

721. Washington Formula. Since 1894 the Engineering Depart- 
ment of the District of Columbia has employed the following 
formula: C = w{lOO - 4p) ^ (6300 + 50p2), in which C = the 



* For a list of many such formulas, see Engineering News, Vol. 63 (lOlO), p. 516-18. 



376 STREET DRAINAGE [CHAP. XIII 

crown in feet, w = the distance between the curbs in feet, and p 
is the longitudinal grade of the pavement in percentage. Notice 
that the crown decreases as the longitudinal grade increases. 

722. Rosewater Formulas. Apparently the formula proposed in 
1902 by Andrew Rosewater, then City Engineer of Omaha, is most 
frequently used. The latest Rosewater formula is as follows: '' The 
crown for asphalt is: C = w (100 — 4p) ^5,000, in which the nomen- 
clature is as in the section next above. For brick, stone block, or 
wood block, the crown is five sixths of that for saphalt." A formula 
for crown formerly used in Omaha gave a less crown than the above 
rule for brick, stone block, and wood block, and a much less crown 
for asphalt. The former formula is : 

for brick, stone block, and wood block, C — (20 — p) -i- 1,600 
for sheet asphalt C = (9 - p) -^ 600. 

The latter formulas are still used by many cities. 

Notice that in the preceding rules the crown is decreased as the 
steepness of the longitudinal grade increases, which is proper. Also 
notice that according to these rules, the crown of sheet asphalt is 
more than that of the other kinds of pavements mentioned, which is 
contrary to the practice of many cities. Considering only the smooth- 
ness of the surface, it appears that asphalt should have the least 
crown; but considering only the fact that asphalt rots when con- 
tinually wet, it appears that asphalt should have a large crown. 

723. The above rules for crown must be modified somewhat 
when the two sides of the street are not at the same elevation — 
see § 693, page 357. 

724. Recommendations of A.S.C.E. Committee. For the crown 
recommended for various road and pavement surfaces by a 
committee of the American Society of Civil Engineers in 1917, see 
Table 16, page 65. 

725. Dished Pavements. The early pavements in this country 
and at present those in some cities in Europe and South America, 
slope from both sides towards the center. In this form the most 
valuable part of the street is devoted to drainage purposes, and it is 
difficult to carry the water to an intersecting street.* The pave- 
ments of alleys usually slope to the center. This form is better for 

♦ The single-gutter Btreet pavement was ably advocated by W. G. Kirchoflf in a paper before 
the Wisconsin League of Municipalities — See Engineering and Contracting, Vol. 44 (1915), 
p. 190-91. 



SURFACE DRAINAGE 377 



alleys than a gutter at each side, since it keeps the storm water from 
flowing along the side of buildings and possibly interfering with Hght 
areas, cellar stairways, etc., and it also carries the water over the 
sidewalk with less annoyance to pedestrian travel. 



CHAPTER XIV 
CURBS AND GUTTERS 

728. Curb. A curb is a plank or slab of stone set at the edge 
of the roadway to protect the sidewalk or tree space and to form 
the side of the gutter. Curbs are not usually set except where the 
street is paved, but they greatly improve the appearance of an 
unpaved street and protect the grass plats at the side of the street, 
particularly during the muddy season. 

Curbs were formerly made of natural stone, but concrete curbs, 
usually combined concrete curb and gutter, are increasing very 
rapidly in recent years — chiefly because of the decrease in the price 
of Portland cement. Natural stone is used now only in the vicinity 
of quarries of suitable stone. Granite is the best natural stone, but 
it is usually very expensive. Limestone and sandstone are fre- 
quently used, but they are generally too easily chipped or broken. 
Concrete unless made with unusual care or protected by steel on 
the edge, is too friable for a business street where heavy loads fre- 
quently back up against the curb. 

729. Stone Curb. Granite curbs are obtained in large quantities 
in several states, notably Maine, New Hampshire, Massachusetts, 
Connecticut, New Jersey, Pennsylvania, Georgia, Wisconsin, Mis- 
souri, South Dakota, CaUfornia. Husdon River bluestone, a variety 
of sandstone commercially known as bluestone, is much used for 
curbs, on account of its hardness, durability, and great transverse 
strength. It Is evenly bedded, splits with a smooth surface, and is 
found in large quantities in the counties of the state of New York 
adjoining the Hudson River from Albany to New York City. The 
sandstones most used for curbs are the following: A gray stone from 
Berea, Ohio; a brownish red stone, known as Medina sandstone, 
obtained in the State of New York on the shore of Lake Ontario; a 
gray, yellow, brown or red stone from Potsdam, N. Y. ; a metamor- 
phic sandstone from Sioux Falls, South Dakota, known as Sioux 

378 



STONE CURBS 379 



Falls quartzite; and a light-pink stone from Sandstone, Minn., 
known as Kettle River sandstone. 

730. The thickness should be sufficient to give strength to resist 
the blows of wheels and to prevent the frost in the earth back of the 
curb from breaking it off at the top of the gutter. The curb is 
usually 4 to 6 inches, depending upon the quahty of the stone and 
the locaUty. The depth must be sufficient to prevent the thrust of 
the earth behind the curb from overturning it, and is usually 18 to 
24 inches. If the sections are too short, it is difficult to keep them 
in place and the general appearance is not good; and if they are too 
long, it is difficult to handle and set them, and nearly impossible to 
get a firm bearing on the bottom. They usually vary from 3 to 8 
feet in length. 

The exposed face of the curb should be bush-hammered or axed; 
and where the sidewalk extends to the curb, the back also should 
be smoothly dressed so the sidewalk maj^ fit closely against the curb. 
The upper face should be cut to a shght bevel with the front face, 
say :|-inch to the foot, so that when the face of the curb is set with a 
little inclination backward, the top face will be level or slope down- 
ward and to the front a trifle. The pavement slopes toward the 
gutter, and therefore a wagon wheel inclines toward the curb; hence 
the curb is set leaning back a little to prevent a wheel from striking 
the face when rimning at the inner edge of the gutter and also to 
secure increased stability. The curb is usually cut with a square 
corner at the outer upper edge; but it would be better if this corner 
were rounded off sHghtly, say to a radius equal to one third of the 
thickness of the curb, to decrease the tendenc}^ to chip. The ends 
of the sections should be smoothly dressed to the exposed depth, and 
the part not exposed should be knocked off so as to permit the dressed 
ends to come into close contact. The ends should fit closelj^ for 
appearance and to prevent the earth, particularl}^ if sand, from run- 
ning from behind the curb between the sections into the gutter, or 
to prevent the sand cushion of a brick pavement from running from 
under the bricks into these cracks and possibly through them into 
holes behind the curb. In a nmnber of European cities, notably 
Brussels, the curb is cut with a tongue in one piece which fits into a 
groove in the next piece, to aid in keeping the curb to line. 

The curb should be set with a uniform batter, in a straight fine, 
and on a regular grade. To fulfill these conditions requires careful 
work in the first place, and to prevent the curb from subsequently 
getting displaced requires proper design and thorough workman- 



380 CURBS AND GUTTERS [CHAP. XIV 

ship. The trench in which the curb is to be set should be dug 4 to 
6 inches below the base of the curb to allow for a layer of gravel on 
which to set the stone; and the width of the trench should be at 
least three times the thickness of the curb to allow room for ram- 
ming the earth around the stone. The bottom of the trench should 
be made smooth and be thoroughly consolidated by ramming, and 
the gravel also should be compacted. Where gravel is expensive, 
it is dispensed with, the curb being set upon brick or stone. In 
filling the trench, the earth should be thoroughly rammed in layers 
not more than 4 inches thick. Where gravel is plentiful, it is some- 
times specified that the trench shall be filled with gravel to 8 or 10 
inches from the top. 

In the past there has been so much trouble in keeping curbs in 
line, that within recent years there has been a general tendency to 
set the curb in a bed of concrete — particularly when concrete is 
used for the foundation of the pavement. A 6-inch layer of con- 
crete is deposited in the trench and the curb set upon it, after which 
the trench is filled with concrete on the street side up to the base of 
the proposed pavement and on the back side nearly up to the top of 
the curb. When set in concrete, the curb does not need to be as 
deep as otherwise, since the concrete then practically becomes a 
part of the curb. 

731. Owing to the difficulty of keeping stone ciu-bs in line or 
rather owing to the expense of setting them so they will certainly 
stay in Line, stone curbs are becoming much less common than 
formerly. They are being replaced by concrete curbs or more fre- 
quently by combined concrete curb and gutter (§ 737). 

732. Cost. In most localities, split sandstone or limestone curb- 
ing 4 to 6 inches thick can be had for 30 to 40 cents per square foot 
f.o.b. cars at the destination; and often sawed stone can be had at 
about the same price. The additional cost of a bush-hammered or 
axed surface will vary with the hardness of the stone and the degree 
of the finish, and curved sections will cost 30 to 50 per cent more than 
straight pieces. Hudson River bluestone (sandstone) curbing 5 
inches thick costs about 30 cents per square foot. Granite curb 
costs from 40 to 50 cents per square foot, depending upon locality 
and thickness. 

For more definite information, see the price reports in current 
technical journals. 

733. Concrete Curb. In some sections where suitable stone for 
curbing is not readily available, curbs have been made of portland 



CONCRETE CURBS 



381 



cement concrete. Owing to the decreasing price of cement, this 
form of curb is coming into more common use. It is usually made 
about 6 inches thick and 18 or 20 inches deep. If well made, it does 
excellently for residence streets. 

For suggestions concerning the construction of concrete curb, 
see § 738^7. 

734. The exposed corner of a concrete curb, particularly on a 
business street, is sometimes protected by a steel angle or special 
form which is anchored to the body of the concrete by lugs or a 
special stem. Several of these forms are very efficient ^ but as they 
are patented nothing more will be said here. For particulars con- 
sult the advertising pages of technical journals. 

735. Cost. Table 37, page 382, shows the cost, as determined 
by 38 time studies, of the concrete curb shown in Fig. 136. It was 
laid in sections 6 feet long with thin metal 
partitions between. At first a 1 : 2 : 5 mix- 
ture was used for the body, but later a 
1 : 2^ : 6; and the facing was 1 : 1^ : l^-. 
The proportions were accurately measured by 
volumes. The concrete was mixed by hand 
on a wood platform in the middle of the street. 
As soon as the concrete had set sufficiently, 
the front forms were removed and the face 
of the concrete was scrubbed with steel 
brushes when the concrete had set hard 
enough to require .them, but usually with 
stiff-bristle brushes. 

736. Gutters. Incidentally the construction of the gutter 
has already been considered in § 709-11, which see. 

Macadam 
Cfnderr 





., — a" — ► 




\ 


t:^':'^^';': 
|^:;•<;/•^: 




faang^ 








5 • • ft . • : : ' 


X 


Concrefe^ > 






;?-;.:• V;yo,:.v;-;:o 






- /-."-'^v'-V' i° 






9" * 





Fig. 136. — Cross Section 
OF Curb. 




Fig. 137. — St. Louis Concrete Gutter or Park Drive. 



Fig. 137 shows a concrete gutter used in St. Louis, Mo., for park; 
drives, 



382 



CURBS AND GUTTERS 



[chap. XIV 



737. Combined Concrete Curb and Gutter. In recent 
years the construction of combined concrete curb and gutter built 
in place has become very general in the smaller cities, and in resi- 



TABLE 37 

Cost of Concrete Curb * 
Superintendence and Over-head Expenses not Included 







Cost Cts. per 


Aver. 


Feet Completed 


:^ 




Lin. Ft. 


per 


PER MAN-HOUR. 


Item 




Amt. 

of 
Total. 






Min. 


Max. 


Aver. 


Min. 


Max. 


Aver. 




Labor: 
















1 


Foreman @ 37|c. per hr. 


1.1 


3.9 


2.2 


4.7 








2 


Water boy @ 10c. " '' 


0.4 


1.3 


0.6 


1.3 








3 


Trenching @ 18c. " " 


2.2 


9.4 


4.9 


10.5 


1.9 


9.6 


4.1 


4 


Placing forms @ 35c. " *' 


1.0 


10.4 


4.2 


9.0 


2.5 


26.4 


7.2 


5 


Removing forms @ 25c. " " 


0.5 


5.2 


1.8 


3.8 


2.0 


38.0 


7.6 


6 


Concrete @ 18c. " " 


2.6 


9.5 


4.3 


9.2 


1.2 


6.8 


3.2 


7 


Facing @ 18c. " " 


0.9 


2.9 


1.7 


3.6 


6.5 


20.4 


10.6 


8 


Finishing @ 35c. '' " 


1.8 


10.7 


4.8 


10.3 


3.7 


20.4 


8.3 


9 


Scrubbing @ 35c. " " 


0.4 


3.4 


1.7 


3.6 


5.0 


48.1 


11.4 


10 


Back-fiUing @ 18c. " '' 
Total for labor 


0.3 


2.0 


1.3 


2.8 


5.9 


51.0 


14.1 


11 


11.2 


58.7 


27.5 


58.8 






Materials: 




12 


Cement @ $1.20 per bbl 


6.2 


8.9 


7.6 


16.2 








13 


Sand @ 0.75 per cu. yd 


1.2 


1.5 


1.4 


3.0 








14 


Gravel @ 1.90 " " " 


6.0 


7.7 


6.9 


14.7 








15 


Facing @ 1.75 " " " 


0.4 


0.7 


0.6 


1.3 








16 


Lumber, 1^-inch spruce 


1.0 


1.0 


1.0 


2.1 








17 


Water, waste, etc 


1.5 


2.0 


1.8 


^3.9 










Total for materials 

Grand Total 




18 


16.3 
27.5 


21.8 


19.3 


41.2 




19 


80.5 


46.8 


100.0 











* Engineering and Contracting, Vol. 43 (1915), p. 61. 

dence districts of larger cities. Such construction is cheap, dur- 
able, efficient, and good in appearance. It is very popular with 
brick and asphalt where the grades are very flat, and is often used 
with a crushed-stone pavement. Fig. 138 shows the cross section 
of the usual form. Notice that the face of the curb is battered. 
This is important, since the pavement is crowned, and therefore the 
plane of a steel wagon-tire is inclined. Consequently if the face of 
the curb is vertical, the tire will strike it at its upper edge; but if the 
face of the curb makes an angle with the pavement greater than 90°, 
the tire will strike the bottom of the curb and do much less damage. 



COMBINED CURB AND GUTTER 



383 



To prevent damage by the striking of steel tires, the curbs to private 
drives, particularly narrow ones, usually have a convex face. 

Fig. 139 shows the form of combined concrete curb and gutter 
employed in St. Louis, Mo. 



2:'Rac(.- 



i::Concreie^ :;• 



l^/operinfQ" 







I ii o Grave/ Concnefe': 



v////Orcrye/orC/ncfer3 ^/ 



£4' 



FiQ. 138. — Standakd Concrete Curb and Gutter. 

738. Foundation. A trench is excavated 4 to 6 inches wider 
than the base of the concrete, and a layer of cinders or gravel 4 to 
8 inches thick (usually 6 inches) is laid, flooded with water, and 
then thoroughly tamped. Upon this foundation is 'greeted the 
forms in which the concrete is to be laid. 



d-o". 









Fig. 139. — St. Louis Concrete Curb and Gutter for Park Drive. 



739. The Forms. There are two general methods of constructing 
these forms: 1. Some contractors lay alternate sections in boxes 
about 6 feet long, and subsequently place boards against the sections 
first laid and construct the remaining sections. This plan is more 
expensive and does not secure as good alignment as the method 
described below. 2. A continuous hne of plank is set for the back of 
the curb and another for the front of the gutter. These planks are 



384 



CURBS AND GUTTERS 



[chap. XIV 



kept in place by stakes on both sides. Partitions are inserted so as 
to divide the mass into sections 6 or 8 feet long. 

Two forms of partitions are in common use. Sometimes these 
partitions are plank 1| or 2 inches thick, in which case the sections 
are laid alternately, the partitions being removed before the second 
series of blocks are formed. In other cases, the partitions are made 
of steel i or 1^ inch thick, and are left in position until the blocks 
are practically finished. There is but little choice in construction 
between the two forms of partitions, except that it is difficult to 
withdraw the steel partitions without chipping the surface — see § 745. 

740. The form for the front of the curb is made by setting a 
plank Ij or 2 inches thick against the front of the upper part of the 
partitions and clamping it to the plank at the back of the curb with 
steel screw-clamps. The lower edge of this plank is rounded to 
make the curve between the face of the curb and the top of the 
gutter. 

The concrete for the base of the gutter is deposited and tamped, 
and then the mortar for the face of the gutter is applied — all before 
the form for the front of the curb is clamped into place. 

741. Mixing and Laying. For information concerning materials 
proportioning, and mixing, see Art. 1, Chapter VII, — Concrete 
Roads.* 

The proportions of the concrete will depend upon the gradation 
of the aggregates (§ 418-24), and upon whether the surface is to 
consist of a richer mixture than the body of the concrete or whether 
the surface is to be finished integral with the body. Usually a 
1:2:4 or al:3:4 mixture is used for the body, and a 1 : li or 
1 : 2 mixture for the facing mortar. 

742. The upper face of the gutter slab is finished by adding a 
1-inch coat of rich mortar and tamping and troweling it, exactly 
as in concrete sidewalk construction. It is important that the sur- 
face of the concrete be free from mud or dust when the topping is 
deposited: and this is a condition quite difficult to secure, because 
the curb and gutter is built in a narrow trench, often a considerable 
distance below the surface, and usually with the excavated material 
piled near. It is also important that the facing be deposited before 
the concrete has begun to set. 



* For a full discussion of the method of testing the cement and proportioning the concrete 
and of the relative merits of gravel and broken-stone concrete, together with tables of quanti- 
ties, strength, cost, etc., see A Treatise on Masonry Construction by Ira O. Baker, 10th edition, 
pp. 745, 6 X9 inches, John Wiley & Sons, New York City. 



COMBINED CURB AND GUTTER 385 

743. There are three distinct ways of finishing the exposed face 
of the curb : 

1. The surface is faced with a rich mortar built integral with the 
body. This may be obtained in either of three ways, of which the 
first is most likely to secure a firm union between the backing and 
the facing, a. A layer of rich mortar is deposited against the lower 
third or half of the front form, and then the concrete backing is 
deposited and both are well tamped; and the process is repeated 
once or twice until the form is full, when the top surface of the curb 
is finished by adding a 1-inch layer of facing mortar, h. A 1- 
inch plank is inserted inside of the front form, and the concrete 
for the body is deposited and tamped; then the 1-inch plank is care- 
fully removed, and a rich facing mortar is tamped into the vacant 
space, c. Instead of the 1-inch plank as above, use a steel plate 
i or ^ of an inch thick having vertical 1-inch angles riveted at 
intervals along its length. This plate is inserted behind the front 
form, the concrete is deposited, and then the facing mortar is depos- 
ited between the front form and the steel plate; next the steel plate 
is removed, and the facing mortar and the concrete are thoroughly 
tamped. 

2. The second method of finishing the face of the curb is to mix 
the concrete rather wet, and spade the face, i. e., after the concrete 
is deposited force a flat spade or its equivalent vertically against the 
back of the front form, and then push the handle away from the 
form to an angle of 20° or 30° and withdraw the spade. If properly 
done, this forces the larger stones away from the face and allows 
enough mortar to flow out against the form to give a solid face and 
permit a good finish of the surface. This makes the strongest face 
of any of the methods; but it is not popular with contractors, since 
to get a soKd face it is necessary to mix the concrete so wet as to 
greatly delay the finishing of the face, which is objectionable for 
several reasons. 

3. Sometimes a rich face is obtained by plastering the surface 
after the forms are removed. But this method necessitates using 
dry concrete in the backing, so as to remove the forms early, and 
consequently is likely to give a weak and porous surface upon which 
to apply the mortar. It is nearly impossible by this method to 
secure a firm union between the plastering and the backing; and the 
plastering is nearly certain to be knocked off by passing wheels 
(particularly during the excavation of the roadway when the passing 
wheels are heavy and the concrete is weak) and to be spalled off by 



386 CURBS AND GUTTERS [cHAP. XIV 

the pressure due to the temperature expansion of the curb. Although 
this method is sometimes used, it should never be permitted. 

744. Finishing the Surface. There is a difference of opinion as 
to whether the surface should be considered finished when it has been 
troweled, or whether it should be afterwards brushed with a slightly 
wet brush. An ordinary flat paint brush, with extra heavy bristles, 
cut off about 1 inch below the wood portion, may be used for this 
purpose. The objections to the trowel-finished surface are that the 
trowel marks show more or less, and that the surface has a glaze or 
shine clearly indicating that the stone is artificial; while the brush 
finish has a uniform dull surface similar to a smoothly dressed natural 
stone. The objections to the brush-finished surface are that the 
brush leaves a porous surface that is not so durable as a trowel- 
finished one, which objection has considerable force if the surface is 
not first thoroughly troweled and if the brush is not used hghtly. 
The less the troweling and the more the brushing, the more rapidly 
the surface can be finished ; and hence it is difficult when brushing is 
permitted to prevent the slighting of the work. Both methods of 
finishing are employed by competent engineers; but the trowel 
finish is more common. 

Recently a method of finishing by drawing a template over the 
curb and gutter has been introduced. The few trials made seem to 
show that this method is a httle less expensive than finishing with a 
trowel, but that it gives a better general appearance and a better 
alignment, particularly at the joints. 

745. Expansion Joints. Concrete curbs and also combined 
curbs and gutters should be built in sections 6 or 7 feet long with 
open joints to allow for expansion. If adequate space for expansion 
is not provided, the compression due to expansion is Hkely to crush 
and sphnter the curb at the joints, and spht off the mortar face or 
the plastering. Many such failures occur. For a discussion of a 
similar problem, see Contraction Joints in the Chapter on Concrete 
Roads (§ 465-68). Sometimes no provision is made for expansion, 
the curb or curb and gutter being made continuous with false joints 
marked at intervals. Sometimes the curb or curb and gutter is 
built in alternate sections without any expansion space between 
adjoining sections, the joints being simply a line of weakness which 
serves to prevent an unsightly crack if a section is displaced by frost 
or by the la teraL pressure of the earth. The curb and gutter should 
be a practically permanent asset, and hence the prevention of its 
destruction by temperature changes is an important matter. One of 



COMBINED CURB AND GUTTER 387 

three means may be employed to prevent failures at the joints of 
curbs and gutters due to expansion. 

1. The gutter flag and the curb are cut into short sections after 
being laid, much as a sidewalk slab is separated into short sections. 
The expectation is that the open joint will afford sufficient space for 
expansion; but it is likely to be filled on the face during the finishing 
of the face of the curb or gutter, which is particularly bad if a mortar 
face is used or if the exposed surface is plastered. Generally the 
open joint is reasonably successful for a time; but is likely to become 
filled with dirt and cease to be effective, and besides the open joint in 
the curb permits the earth behind the curb to escape, or with brick 
or block pavements the open joint in the gutter permits the sand 
cushion to escape. 

2. Instead of cutting the curb and gutter as described in the 
preceding paragraph, it is nmch more common to insert steel dia- 
phragms or partitions in the forms at intervals of 6 or 7 feet, which 
are withdrawn as the face of the curb and gutter is finished. These 
partitions are usually i or 3^ inch thick. This joint is more efficient 
than the one described above, and is easier to construct; but it 
is open to substantially all of the objections to the preceding one. 

3. Occasionally partitions consisting of one or two thicknesses 
of tar paper or one thickness of tar or asphalt felt are inserted in the 
forms at intervals of 6 or 7 feet; and after the face of the curb and 
gutter has been finished the paper or felt is cut off with a sharp knife 
a little below the surface of the concrete. 

746. Whatever the method of constructing the expansion joint, it 
should be in a vertical plane perpendicular to the face of the curb, or 
one section may push past the other. 

With any form of expansion joint, there is danger that the expan- 
sion of the straight curb will dislocate the curved curb at the corner 
of the block and at the alley return. This can be prevented by 
making an extra wide expansion joint near the corner. This joint 
may be ^ to 1 inch wide according to the length of the block and the 
temperature when the curb is constructed; and it should be filled 
with tar pitch or asphalt. A number of proprietary compounds are 
upon the market for this purpose, made in sheets of different thick- 
nesses. 

747. Curbs are frequently damaged by being pushed over or 
broken by the expansion of cement walks. The remedy is to insert 
an expansion joint between the end of the walk and the back of the 
curb, or better in the joint in the walk one section back from the curb. 



388 CURBS AND GUTTERS [CHAP. XIV 



The expansion joint may be filled with tar paper or felt; or a thin 
board may be inserted during the construction, and after the con- 
crete has set the board is withdrawn and the space is filled with tar 
•pitch. The joints must occasionally be re-filled — preferably once 
each year. 

748. Cost. The cost will depend upon the price of labor and 
materials, and upon the proportions of the mortar of the face and 
the concrete of the body. The amount of cement required will vary 
a Httle with the percentage of voids, but will depend chiefly upon the 
proportions of the mortar and the concrete. 

The following data are for laying more than a mile of combined 
curb and gutter of the form shown in Fig. 138, page 383. The pro- 
portions of the facing mortar was 1:2; and that of the concrete 
1:3:4 washed gravel. A barrel of portland cement made enough 
1 : 2 mortar for the facing on 33 linear feet. The length of finished 
curb and gutter laid with a barrel of cement was 16 feet, with a varia- 
tion of 1 per cent either way on different days. A yard of sand and 
pebbles laid 18 lineal feet. The loss of gravel in transportation and 
handhng, and the shrinkage in tamping was nearly uniformly 20 
per cent. The average length of curb and gutter completed, includ- 
ing straight work and curved returns at streets and alleys, and also 
including excavation, per man per hour was 0.333 foot. The trench 
was excavated before the roadway was excavated. The concrete 
was mixed in a batch mixer which discharged directly into the 
trench. The two finishers received 60 cents per hour, the three men 
setting face forms 35 cents, and the remainder 25 cents. The work- 
ing force of 18 men when constructing forms and laying curb and 
gutter was divided as follows: 

1 foreman and finisher, 

1 finisher, 

2 men setting face forms, 

3 men setting back forms, 

2 men wheeling and tamping cinders, 
2 men running concrete mixer, 
2 men feeding concrete mixer, 
2 men mixing face mortar by hand, 
1 man wheeling facing mortar, 
1 man spreading facing mortar, 
1 boy carrying water, etc. 

The contract price in 1916 for the curb and gutter, including 
excavation and back filling, was 50 cents per lineal foot. 



COMBINED CURB AND GUTTER 



389 



749. Double Curb and Gutter. Fig. 140 * shows the details of 
the form of the concrete double curb and gutter referred to in Fig. 
114, page 357. 




Fig. 140. — Double Curb and Gutter, 

750. Curb and Gutter at Private Driveway. Fig. 141, page 390, 
shows the arrangement of the combined concrete curb and gutter 
at a driveway to a gate or a building. The radius of the curve at 
the corner of the curb is too small, as a radius of 4 or 5 feet would be 
better. 

751. Merits of Concrete Curb and Gutter. The advantages 
of the combined concrete curb and gutter are: 1. It is usually 
cheaper, particularly if account be taken of the fact that the gutter 
occupies space that otherwise would be paved. 2. The alignment 
of the curb is better and more permanent. 3. The appearance 
is better. 4. Usually the concrete is more durable than a natural 
stone of equal cost. 5. The gutter is smooth, and easily cleaned. 

A concrete curb is suitable only for residence streets, but is more 
durable for a business street than soft sandstone or limestone. 

752. Other Forms of Curbs. About 1889 there was con- 
structed on two streets at Washington, D. C, a concrete curb and 
gutter having at the inner lower edge of the curb a 4X 4-inch con- 
duit for telegraph and telephone wires, with hand holes about 50 
feet apart. The experiment was not considered successful, and the 
conduit was never used for wires. 

From time to time advertisements appear of burned clay curbs; 
but none have been seen which are not so thin as to be easily broken, 
and so constructed by sections fitted together as to be unstable. 

753. Radius of Curb at Street Corner. As far as vehicular 
traffic is concerned, the larger the radius of the curb the better; 



* Trans. Amer. Soc. of Civil Engineers, Vol. 42, p. 7. 



390 



CURBS AND GUTTERS 



[chap. XIV 



but when the gutter is carried to a corner inlet (§ 705), it is incon- 
venient to construct or cover the gutter if the curved curb intersects 
the sidewalk, i. e., if the radius of the curved curb is too great. If 
the pavement has the minimum width, say 18 or 20 feet, the curves 
of the corner curbs should be made large so that a vehicle may be 
turned around at the street intersection. 




PLAN 




Section A-B 




Section C-D- 
Fig. 141. — Concrete Curb and Gutter at Private Driveway. 



Formerly, when curbs usually were natural stone, the cost of 
curved sections was considerably more than that of straight pieces ; 
and hence the tendency was to keep the radius as small as possible. 
But now that concrete curb is very common, curved curbs cost only 
a little more than straight ones. Formerly, when most of the vehic- 
ular traffic was horse-drawn, the chief objection to a short radius was 
the wear due to wheels striking the curb at the corner; but now on 
streets having any considerable motor-driven traffic, a corner curb 



RADIUS OF CURB AT CORNER 391 

having a short radius makes it nearly impossible for a motorist to 
maintain a reasonable rate of speed in turning the corner and at the 
same time keep his machine on the right side of the street. 

The radius varies from 2 to 12 feet, usually from 6 to 8 feet. The 
curb with a 2- oot radius should not be used at a 1, or at least only at 
driveways to private grounds. A radius of 10 to 12 feet is usually 
satisfactory; but on boulevards or streets where there is consider- 
able automobile travel, a radius of 16 or even 20 feet is desirable. 
Several cities have recently spent considerable money to increase 
the radius of the corner curbs, particularly on main traveled streets 
and boulevards, to the satisfaction and safety of automobihsts. 

754. Combined Curb and Walk. In Chicago a concrete 
walk about 1 foot wide has been constructed along the curb in front 
of a large apartment building, so as to permit vehicles to stop any- 
where along the curb to discharge or receive passengers. Such a 
walk has been found to be a great convenience. 



CHAPTER XV 

FOUNDATIONS FOR PAVEMENTS AND STREET-RAILWAY 

TRACKS 

757. The term foundation is sometimes applied to the natural 
soil upon which an artificial structure rests, and sometimes to the 
lower portion of the structure itself. The term will be employed 
here in the lattpr sense, and the soil under the foundation of the 
pavement will be referred to as the subgrade. 

The foundation of a pavement, as of all other structures, is an 
important element, although it is more frequently neglected in pave- 
ments than in other structures. 

One of the most perplexing problems in connection with pave- 
ments is the construction and maintenance of a pavement adjoining 
a street-railway track that is durable and does not interfere unduly 
with travel. Part of the difficulties are due to the foundation and 
part to the construction of the pavement adjacent to the rails. The 
former will be considered in Art. 3 of this Chapter, and the latter in 
connection with the discussion of the different kinds of pavements. 

Aet. 1. Peeparation of the Subgeade 

758. Whatever the form of the pavement or of its foundation, it 
must rest upon the soil; and snce the chief office of the pavement 
and of its foundation is to distribute the concentrated load of the 
wheel over an area so great that the natural soil will be able to 
support it, it is important to ncrease, as much as practicable, the 
bearing power of the soil by drainage and by roUing, and thereby to 
decrease the thickness of pavement required. 

759. Drainage. The method of draining the subgrade of a 
pavement is substantially the same as that of underdraining an 
earth road — see § 114. The subgrade of a pavement requires under- 
drainage fully as much as does an earth road, notwithstanding 
the fact that the former has an impervious roof, The purpose 

392 



ART. 1] PREPARATION OF THE SUBGRADE 393 

of the underdrainage is to prevent the surface of saturation from 
rising so high as to soften the subgrade. Unless the subsoil is very 
open and porous, it is economical to lay a tile under each edge of 
the pavement, 2 or 3 feet below the surface of the subgrade. This 
tile may empty into the surface-water catch basins (§ 703). 

760. Earthwork. The machinery employed in making exca- 
vations and embankments for pavements is practically the same 
as that used in constructing earth roads — see § 148-57. 

In making embankments great care should be taken to com- 
pact them solid — see Shrinkage of Earthwork (§ 140), Settlement 
of Embankments (§ 141), Rol ing Embankments (§ 143), and Sta- 
bihty of Embankment (§ 146). For data on the Cost of Earth- 
work, see § 164-87. 

The excavation for pavements is made by plowing and then 
removing the earth either with a drag or a wheel scraper (§ 150, 154), 
or by loading it into wagons or carts with hand-shovels. The 
subgrade, even though on'y a comparatively thin layer is to be 
removed, has recently been excavated and loaded into wagons with 
a steam shovel usually of the revolving type; and more recently 
the excavation has been made with the four-wheel scraper (§ 154) 
drawn by a steam engine while being loaded. It is usual to specify 
that no plowing shall be allowed within 2 inches of the subgrade, to 
prevent the soil below the subgrade from being loosened. If the 
subgrade is thoroughly rolled, as described later, plowing a little 
below the finished surface is not a serious matter; but if the sub- 
grade is not subsequently well rolled, the loosening of the soil below 
the finished surface is very objectionable, since the foundation will 
then have an uneven hardness. 

The subgrade is often finished 
with pick and shovel, but the 
work can be done much more 
economically with the scraping 
grader (§ 155) or with the sur- 
face grader. Fig. 142. The former 
makes a more uniform surface, 
and is usually more economical; 
although the latter is an effective fiq. 142.— surface gradeb. 

implement. In either case the 
loosened earth must be hauled away with scrapers or wagons. 

762. A considerable part of the excavation is often done before 
the curb is set, but the curb is always set before the subgrade is 




394 FOUNDATIONS FOR PAVEMENTS [cHAP. XV 

finished. The exact position of the subgrade is determined by 
stretching a string transversely across the street from curb to curb 
and measuring ordinates similar to those shown in the upper dia- 
gram of Fig. 135, page 375. Some contractors pick narrow trenches 
down to the subgrade at short intervals transversely across the 
street; while others drive stakes with their tops a specified dis- 
tance, say 4 or 6 inches, above subgrade, and provide the work- 
men with a stick of this length with which to measure down from 
the top of the stake to the subgrade. The former method must 
be employed when the scraping grader is used. The passage 
of the grader fills the trench with loose earth, but it is easy 
to see the relative position of the surface and the bottom of the 
trench. 

763. Rolling the Subgrade. The finished subgrade should 
be thoroughly rolled to consohdate the surface and also to discover 
any soft places — particularly over trenches that have not been solidly 
filled. If the roller reveals a low place, it should be filled with earth 
and be rolled again. The roller, whatever its weight, should be 
passed over the subgrade more than once, since the successive pas- 
sages have something of a kneading action and add to the solidity 
of the soil. Several passes with a light roller give better results than 
a few passes with a heavy one. It is well to specify both the weight 
of the roller and the number of times it is to pass over the road-bed. 
For some hints apphcable in rolHng the subgrade, see § 369. 

Formerly a horse roller was sometimes used for this purpose; 
but a steam or rather a self-propelled roller (§ 378) is much better 
because it is heavier, and, still more important, because with it the 
street can be rolled transversely. The street is full of trenches made 
often just before the pavement is laid, in connecting the houses with 
the sewer, the water, and the gas; and as these trenches rim both 
longitudinally and transversely, it is necessary to run the roller in 
both directions if the trenches are certain to be sohdly filled. 

Unless the back-fiUing of a trench has been unusually well tamped, 
a roller run transversely over a trench will leave a depression. In 
most soils, the back-filling will not of itself settle into its former 
sohdity, however long it is left to the action of traffic and to the forces 
of nature; and whatever the foundation of the pavement, the heavier 
traffic is nearly certain to cause a settlement over these same trenches, 
unless the subgrade is well rolled. Traffic consoHdates only a thin 
layer near the surface which is usually removed when the pave- 
ment is constructed. Ordinarily, if the subgrade is rolled both longi- 



ART. 2] PREPARATION OF THE SUBGRADE 395 

tudinally and transversely with a roller weighing 10 or 12 tons, 
there will be no settlement of the pavement. 

In rolling, if a depression is produced over a trench, it should 
be filled and then again rolled. If the depression is of considerable 
depth, it shows that the trench was badly filled or was very deep, 
or both; and therefore it is wise to re-consolidate the trench. One 
way of doing this is to make numerous openings through the crust 
and keep the depression filled with water until the earth in the 
bottom of the trench has become thoroughly soaked; and then 
after the ground has dried out below, the roller should again be passed 
over the surface. The surest way to prevent settlement over trenches 
is to pack the soil solidly when the trench is first filled. For a dis- 
cussion of various methods of back-filling, see § 764. 

Insufficient tamping in filling trenches or inefficient rolling 
of trenches is a very common defect in pavement construction, 
nearly every block presenting one or more such depressions. One 
of the purposes of a guarantee of the pavement (§ 652) is to secure 
a thorough consolidation of the soil in the trenches. 

764. FILLING TRENCHES. The back-filling of trenches opened 
to lay water and gas pipes, to make house connection to sewers, 
etc., so that the road surface shall be restored to its former level 
and remain so, is a matter of importance on both paved and un- 
paved roads — particularly the former. The failure to re-fill the 
trenches properly is a source of annoyance to those who use the 
impaved road and of damage to the pavement. It is frequently 
asserted by those having opportunity for knowing, that the dam- 
age to pavements through lack of care in re-filling trenches and 
re-placing the pavements is greater than the wear due to traffic. 
No kind of municipal work should be more rigorously inspected 
than the filling of a trench over which a pavement is to be laid. 
The nearly universal result of a neglect in this respect is that a 
pavement built at great expense is disfigured or damaged by settle- 
ment, the repair of which will cost many times as much as it would 
have cost properly to fill the trench originall}^ 

The principal cause of failure is lack of care; but sometimes it 
is due to a mistake as to the proper method to be employed. A 
discriminating judgment is required to determine the proper method, 
and intelligence and faithfulness are necessary in carrying it out. 
There are several distinct methods used in consolidating the back- 
filling of trenches. 

765. Natural Settlement. A common practice of those having 



396 FOUNDATIONS FOR PAVEMENTS [CHAP. XV 

occasion to make excavations in unpaved streets is to cast back 
loosely the material taken out, heaping it into an unsightly and 
annoying ridge over the trench and trusting to travel and the ele- 
ments to restore the surface to its original level. In nearly" pure 
sand such a ridge may in time settle to the original level, although 
the damage due to the temporary ridge will generally be much 
more than the cost of properly filling the trench in the beginning; 
but as a rule loam or clay loosely put back will not attain a sufficient 
degree of compactness to make it a safe support for a macadam or 
other form of pavement. The surface may become very compact 
and hard; and yet after the removal of a foot or more of soil, 
ordinarily necessitated by the construction of the pavement, it will 
be found that the earth in the trench will settle considerably imder a 
roller run transversely over the trench. Even though the surface 
may support the roller, it is highly probable that ultimately a trench 
which has been loosely filled will settle and cause a depression in the 
pavement. This is proved by the numerous depressions in pave- 
ments, and also by the fact that when trenches loosely filled are 
opened years afterwards, it is very common to find open cavities. 
The promptness with which natural settlement takes place depends 
upon the cHmatic conditions and the underdrainage. It is never 
safe to depend upon natural settlement to secure the proper com- 
pacting of the soil in trenches over which a pavement is to be laid, 
however long the time allowed for the settlement, and much less 
the few weeks often specified. 

766. Flooding. Where the water can be had cheaply, it is a 
common practice to attempt to consoHdate the earth in the trench 
by flooding or puddhng it. If the soil is sand or gravel and is so 
pervious that the trench will drain out rapidly, thorough flushing 
will compact the material so that no trouble will be experienced 
with settlement; but the flushing must be done thoroughly. It 
is not sufficient to fill the trench nearly full of loose material, and 
then turn on a gentle stream of water until the trench is full; for 
trenches thus filled are certain to settle later. The sand or gravel 
should be added in layers not more than 8 or 10 inches thick, and 
each layer should be flushed with a stream of water having force 
enough to wash the finer particles into the voids between the larger 
ones. Substantially the same result may be accomplished by 
shoveling the sand or gravel into water 8 or 10 inches deep; but 
this method will not be effective, if the trench is filled with a scraper 
or a scraping grader. 



ART. 2] PREPARATION OF THE SUBGRADE 397 

However, wherever flushing is effective, tamping would be 
equally as good and would probably be less expensive, if the cost 
of the water be considered. As a rule attempting to consolidate 
trenches by flooding is bad practice. 

Neither of the preceding methods of using water should be 
employed with clay or clayey soils, since flushing prevents rather 
than assists the consolidation of such soils. In other words, flush- 
ing or puddling is useful only with soils which water readily breaks 
down. If clay is flooded or is deposited in water, the trench is filled 
with a watery mud that will shrink very much as it dries out and will 
always be loose and porous. It is well known that a stiff-mud 
brick which has been moulded under exceedingly heavy pressure 
will shrink in drying 5 per cent, and with some clays 10 per cent; 
and of course the thin clay mud in a flooded trench will shrink very 
much more than this. 

767. Tamping. Except in the ease of comparatively clean 
sand and gravel, back-filling can be thoroughly done only by tamp- 
ing; and to make this method successful it is necessary (1) that 
the material shall be moist enough to be plastic, but neither too wet 
nor too dry, (2) that it shall be deposited in layers not more than 
3 or 4 inches thick, and (3) that each layer shall be thoroughly tamped. 
To secure thorough tamping the relative numbers of tampers and 
shovelers is sometimes specified; but this alone is ineffectual since 
there is a natural tendency for the tampers to work less energetically 
than the shovelers, and besides more labor is required to tamp the 
soil around the pipe than higher up. 

The amount of ramming required will vary with the character 
and condition of the soil. Clay and hard pan should be moistened 
before being tamped, while clean sand or clean gravel may be tamped 
dry. The tamping can be most effectively done with a compara- 
tively small light rammer or tamper, since the effect of the blow 
is transmitted to a greater depth, while a broad heavy rammer 
consolidates the surface only. A tamper weighing 5 or 6 lb. is better 
than one weighing 20 or 25 lb., the lighter one being lifted higher 
and giving less fatigue than the heavy one. It is important to 
remember that any amount of ramming will affect only a compara- 
tively thin layer. 

Obviously back-filUng should not be attempted when the mate- 
rial is frozen, since subsequent settlement is then sure to take place. 
768. To prevent disturbing the surface of a pavement, plumbers, 
gas fitters, etc., are sometimes given permission to tunnel under 



898 FOUNDATIONS FOR PAVEMENTS [cHAP. XV 

the pavement to make their connections. This practice is never 
justifiable on account both of the excessive cost and of the impos- 
sibiUty of effectively filling the tunnel, owing to the limited space 
in which the work must be done. In nearly every case a depression 
occurs sooner or later over the tunnel. 

769. Replacing All the Material. The result to be obtained 
in fiUing a trench is that the material in the trench shall have the 
same compactness as the soil around it; and therefore some con- 
tend that the only proper way is to put back all the material taken 
out. In a majority of cases this procedure will secure reason- 
ably good results; but under certain conditions it will fail. For 
example, the water pipe or sewer may occupy a large proportion 
of the volume of the trench, and consequently of necessity there 
will be a considerable excess of earth. Again, putting back all 
the earth does not insure the. restoration of the original surface 
nor certainly prevent subsequent settlement. It has been shown 
that soil when taken from its natural place and compacted in an 
embankment will shrink from 8 to 15 per cent (see § 140), and 
will probably subsequently settle 2 or 3 per cent and possibly 10 to 
25 per cent (see § 141). Consequently with a deep trench con- 
taining a small pipe, it is possible to tamp the earth back so solidly 
as not to have enough to restore the surface; or it is possible to 
put all the soil back by tamping the lower portion of the trench 
soHdly and the upper portion loosely, and still considerable settle- 
ment take place. Therefore the specification to re-place all of the 
material, must have a careful and intelligent supervision to insure 
good results. 

In the past it has not been the custom to fill trenches in such 
a manner as to prevent settlement; and therefore if the best results 
are to be insisted upon, the specifications should clearly reveal that 
fact, for contractors in bidding on work do so on the understanding 
that the work is to be done in at least approximately the usual 
manner, and any attempt to have it done in any better way, which 
was not clearly understood from the beginning, is likely to cause 
friction and irritation, and possibly finally to result in failure. 

770. Re-filling with Sand or Concrete. On account of the dif- 
ficulty of getting trenches in clay or loam filled so that there will 
be no settlement, it has been proposed to require the trench to be 
filled with clean sand or gravel. It is not known that this method 
has ever been tried. It would probably be effective, but usually 
its cost would be prohibitive. 



ART. 2] THE CONSTRUCTION 399 

In at least a few cases trenches have been filled with a fair qual- 
ity of hydraulic cement concrete. The expense for the concrete 
was not justifiable, since it was much greater than that required 
thoroughly to tamp the back-filling. 

Sometimes municipal authorities are lax in inspecting the filling 
of trenches, owing to the belief that the concrete foundation will 
hold up the pavement even though the material in the trench may 
settle; but this is bad practice, since the ordinary thickness of con- 
crete is not designed to act as a bridge, and besides if it is thick 
enough to bear up over trenches it is needlessly thick elsewhere. 
With the usual thickness of concrete foundations, a depression is 
almost certain to occur if the material in the trench settles; and 
hence the only safe rule is to have the trenches completelv and 
compactly filled. 

Art. 2. The Construction 

772. In some cases a pavement has been laid directly upon the 
natural soil; but this is possible only with brick, stone-block, or 
wood-block pavements laid upon clean sand or gravel. This prac- 
tice is wise only with light travel. Formerly in Cleveland, Ohio, 
many brick pavements were laid directly upon the native sand. 

Stone-block and brick pavements were formerly laid upon a layer 
of gravel or broken stone; but the decline in price of hydrauHc cement 
has made it economical to substitute concrete for the layer of gravel 
or broken stone, owing to the labor and care required to secure a 
bed of uniform density and smooth surface. 

A layer of portland cement concrete is now the nearly universe! 
foundation for street pavements. 

773. Portland-Cement Concrete Foundation. This is 
by far the most common foundation for pavements. The advan- 
tages of such a foundation are : 1 . It gives a smooth uniform surface 
upon which to lay the pavement. 2. It prevents the surface water 
from percolating to the subgrade. 3. By its thickness and resistance 
to flexure, it distributes the concentrated load over a considerable 
area of the subgrade. 4. Concrete acts as a bridge to support the 
pavement in case of a settlement of the subgrade. 5. Being imper- 
vious to water and a non-conductor of heat, concrete protects water 
and gas pipes from freezing. 

774. The Materials. For a discussion of the cement, the sand, 
and the gravel or broken stone as ingredients for concrete, see Art. 1 
of Chapter VIL 



400 FOUNDATIONS FOR PAVEMENTS [CHAP. XV 

775. Thickness. The thickness of the concrete varies from 4 to 
8 inches, but is usually 6 inches. There is considerable diversity of 
opinion as to the sufficiency of a 6-inch concrete foundation, par- 
ticularly since the introduction of motor trucks. Examples are 
frequently cited of the failure of a concrete foundation, particularly 
where a motor truck or heavily loaded wagon has broken through a 
pavement; and the conclusion is drawn that the concrete slab was 
too thin. However, making the foundation thicker is not neces- 
sarily the economical remedy. The foundation may have failed 
for one or more of the following reasons: 1. Insufficient rolUng of the 
subgrade. 2. Insufficient consolidation of back-filHng in trenches. 
3. The use of natural cement in the concrete, which is weaker than 
Portland cement and lacks uniformity. 4. Improper proportions, 
insufficient mixing, or inadequate curing of the concrete. As a rule 
insufficient attention is given to each of these items. 5. Passage of 
loads over the concrete before it had sufficiently set. 6. Vibrations 
due to weak construction of street railway track, which shatter the 
concrete and allow water to get under the foundation which upon 
freezing still further cracks the concrete. 

On the other hand, many examples can be cited where a 4-inch 
concrete base has successfully carried a heavy traffic. It is prob- 
able that a well-constructed slab 4 inches thick laid on a well-con- 
solidated subgrade is stronger than a foundation of poor concrete 
8 inches thick laid upon an insufficiently rolled subgrade.* 

776. In view of the rapid introduction of the motor truck and the 
consequent crushing of some pavement foundations, it is probable 
that concrete pavement foundations should be improved in quality 
or increased in thickness — or perhaps both. The question of im- 
proving the quality depends upon the relative cost of materials and 
labor; and the advisability of increasing the thickness can be deter- 
mined only by a discriminating study of the experience with a par- 
ticular thickness. 

777. The thickness of concrete roads (§ 447) gives some indica- 
tion as to the required thickness of concrete pavement foundations, 
although the former are ordinarily more carefully constructed than 
the latter. The thickness of concrete roads is usually about 6 inches, 
and is seldom more than 6 inches at the sides and 8 inches at the 
center, the excess thickness at the center being to provide for reduc- 



* For a discussion of this subject, pro and con, see Engineering News, Vol. 72 (1914), p. 
176, 367, 558, and 1033; and Vol. 75 (1916), p. 1097. 



ART. 2] THE CONSTRUCTION 401 

tion by wear. The wearing coat adds thickness to the pavement, 
which distributes the wheel-load over a greater area of the sub- 
grade, and some kinds of wearing surfaces also give additional beam 
strength to the pavement as a whole. For example, the binder and 
wearing coat of a sheet asphalt pavement adds 2J or 3 inches in 
thickness, and gives considerable additional beam strength. Again, 
a portland-cement grouted brick wearing-coat has been found to 
give so much additional beam strength that the total thickness of 
the pavement has been greatly reduced in recent years (see § 1028- 
30). 

778. It has been proposed to limit motor trucks to certain streets, 
rather than build all pavement foundations heavy enough to carry 
such loads. There would be some justice in such a requirement, but 
the enforcement of it would be difficult. 

779. The Proportions. For a discussion of the theory of pro- 
portioning concrete, see § 417-24, Chapter VII — Concrete Roads. 

The proportions of the concrete for a pavement foundation is 
usually determined arbitrarily without much, if any, reference to the 
gradation of the coarse and fine aggregate. The proportions and 
sizes of the aggregate specified by a number of important cities 
whose specifications happened to be at hand, are as follows : 



Proportions 


Sand 


Stone 




H:2i 


i" to fine 


i" to 1" 




U:3 


I to fine 


I toll 




2 :3 


1 to fine 


1 toll 




21 : 4 


I to fine 


I toll 




3 :5 


i to fine 


1 to 2 




3 :6 


I to fine 


1 to 2 



The last proportions seem to be much the most used. It may be 
that with the aggregates ordinarily employed in each case, the 
proportions specified will give a good concrete; but the quality 
of the concrete can not be foretold from the above specifications. 
To secure the best results the proportions should be determined, or 
at least tested, by a sieve analysis (see § 422) ; and to make the spe- 
cifications really significant both the proportions and the gradation 
of the aggregates should be stated. 

For the proportions used in concrete roads see § 444. However, 
it is not customary to use as rich a mixture in concrete pavement- 
foundations as in concrete wearing-surfaces; and under ordinary 
conditions, it is not necessary. 



402 FOUNDATIONS FOR PAVEMENTS [cHAP. XV 

780. Mixing. All that is said in § 451-58 concerning the mixing 
of concrete for concrete roads, applies to concrete for pavement 
foundations. 

781. Placing. If the subgrade has been rutted up by ordinary- 
travel or in the delivery of paving materials, the surface should 
be restored; and if the surface has been much disturbed, the sub- 
grade should be again rolled. The ridges thrown up at the sides of a 
wheel track may materially weaken the concrete foundation. Under 
ordinary circumstances the subgrade should be sprinkled just before 
the concrete is laid. This will prevent the dry subgrade from 
absorbing moisture from the concrete, and will also prevent its drying 
out too fast. 

It is important that the surface of the concrete shall conform to 
the required grade and crown. The thickness may be indicated by 
grade stakes set every 4 or 5 feet. Some engineers require the con- 
crete to be struck off with a template which may run upon the curbs 
or upon screeds carefully placed for that purpose. 

The edge of the concrete should form a straight line from curb to 
to curb perpendicular to the line of the street. 

782. No contraction joints are provided in concrete pavement 
foundations as in concrete roads, since the latter are not as much 
exposed to temperature changes as the former. 

783. Finishing. The concrete should be tamped to consoUdate 
it. The wetter the concrete, the less the tamping needed; and 
usually there is very little tamping. Many engineers claim that the 
concrete is ordinarily unduly weak because it is mixed unduly wet. 
If the concrete is not mixed too wet, the proper tamping or ramming 
of the concrete will consolidate it and fill the voids, and add mate- 
rially to its strength. Until recently it was the usual custom to 
finish the concrete foundation by light tamping; and often the sur- 
face was unduly rough. In defense of this practice it was claimed 
that the rough concrete prevented the shifting of an asphalt pave- 
ment; and that with brick, stone-block, and wood-block pavements 
the roughness of the concrete did no harm, as the cushion layer 
gave a smooth surface upon which to place the pavement. In 
neither case is the claim valid. A sheet asphalt pavement upon 
such a foundation will creep and form waves or humps because of 
the difference in compression due to its unequal thickness ; and it has 
been conclusively established that the thinner the cushion course the 
better for any brick pavement (see § 971) or block pavement (see 
§ 109G). The utmost roughening of the surface of a concrete base of 



ART. 2] THE CONSTRUCTION 403 

sheet asphalt pavement should be that produced by a sHght raking 
while the concrete is fresh; and for all other kinds of pavements, 
the smoother the finish the better. 

Sometimes the surface of the concrete is grouted, that is, a rich 
mortar is poured upon the surface and swept over it to level up any 
depression and to fill up any honeycombing. Sometimes the surface 
is broomed without the pouring on of any grout, the surplus mortar 
being swept from one part of the surface to level up depressions and 
to fill up, or rather hide, honeycombing. The term slushing is 
sometimes applied to each of these processes. No such method of 
finishing the surface should ever be permitted; although in extreme 
cases concrete made of fine stone in the stated proportions may be 
used to level up depressions. 

Some engineers claim that the surface of a concrete base should be 
floated to secure a uniform smooth surface upon which to lay asphalt- 
block or wood-block pavements. With a brick pavement the same 
result is accompHshed in another way (see § 982). 

Not infrequently loose stones are left on the upper surface of the 
concrete foundation while laying the binder course of a sheet asphalt 
pavement or the cushion course of a brick or block pavement. Such 
a practice is inexcusable, since the labor to remove such stones is 
slight, and since they have a seriously destructive effect upon the 
wearing coat. 

784. Curing. In building concrete roads, it is nearly universal 
after the concrete is laid to protect it during curing by covering it 
with canvas, or damp earth, or a sheet of water (see § 464); but in 
constructing concrete pavement-foundations, it is quite unusual 
to take any such precautions, and consequently the concrete is 
frequently seriously damaged by drying out too rapidly in hot or 
windy weather, or by exposure to low temperature. 

The period during which the concrete base should be allowed 
to harden will depend upon the weather conditions and the kind 
of pavement to be laid upon it, or rather upon the method of delivering 
the subsequent paving materials. Teaming over the concrete in 
building the remainder of the pavement should never be permitted 
in less than 10 to 15 days, depending upon the weather; and the 
pavement should not be open to heavy loads in less than 15 to 21 
days from the time the concrete foundation was laid. The pressure 
to shorten this time is often very great, particularly on a business 
street. 

785. Cost of Concrete Foundations. Materials. The cost of 



404 FOUNDATIONS FOR PAVEMENTS [CHAP. XV. 

materials varies with the locahty and the conditions of the markets 
(see § 425-27) ; and hence it is unwise to cite examples except as in 
§ 790. When the prices are known, estimates may be easily pre- 
pared by the use of Table 28, page 237. 

786. Labor. Formerly concrete for pavement foundations was 
mixed by hand; but in recent years it is almost always mixed by 
machine. 

787. Hand Mixing: The following data on the labor-cost of 
hand-mixing are out of date as to the method of mixing and also as 
to the cost of labor; but as the price of labor is stated, these data may 
be useful in making estimates when hand mixing is to be employed. 

In a small western city the average cost to the contractor of 
mixing and laying a thickness of 6 inches of concrete during two 
years was about 7 cents per square yard, for 1 part cement, 2 parts 
sand, and 4 parts broken stone, turned six times exclusive of casting 
into place. With gravel instead of broken stone the cost was about 
6 cents per square yard; and with four turnings instead of six, the 
cost was about half a cent less than the prices above. All the mixing 
was done with shovels. The wages of common laborers was $1.50 
for 10 hours. 

In a large western city the average cost to various contractors 
of mixing and laying a thickness of 6 inches of concrete was 5i 
cents per square yard. The mixing was done with hoes, the specifi- 
cations requiring that the concrete should be mixed until each 
particle of the stone was completely covered with mortar. The 
wages of common laborers was $1.50 for 10 hours. 

778. The following example * gives the distribution of the labor 
of la3dng a 6-inch concrete pavement foundation, in hours per square 
yard: 

Items. Houes 

PER Sq. Yd. 

4 men filling barrows with sand and stone 0.15 

10 men wheeling, mixing, and shoveling to place (3 or 4 steps) . 37 

2 men ramming . . 07 

1 water boy, equivalent in common labor . 01 

1 foreman, equivalent in common labor . 06 

Total hours per square yard . 67 

The sand and stone were dumped in the street upon boards, and 
were hauled in wheel-barrows about 40 feet to the mixing boards. 

* Engineering News, Vol. 46 (1901), p. 424. 



ART. 2] THE CONSTRUCTION 405 

The mortar was turned three, and the stone three or four times. 
Two gangs under separate foremen worked side by side in the same 
street. 

The same correspondent gives another example which required 
0.56 hour per sq. yd., in which case the mortar was turned only 
once and the stone twice, water being used in abundance. 

The cost of labor in mixing and laying concrete is often 8 or 9 
cents a square yard. For the most economical work the sand and 
stone should be deposited in ridges on the subgrade near the middle 
of the street; and if they are piled on the parking, the cost will be 
considerably greater than above. 

789. For data on cost of hand-mixed concrete for concrete roads, 
see § 374. 

790. Total Cost. The total cost of a concrete pavement-foun- 
dation laid in a city in the Central States in 1916 was as follows: 

Items Cu. Yd. Sq. Yd. 
Subgrade : 

Rough grading,— 1,504 cu. yd $0,298 

Surfacing and rolling 3,380 sq. yd., and cleaning up . 090 $0 . 040 

Miscellaneous expense . 036 . 009 

Total, exclusive of superintendence, depreciation on 

machinery, administration $0,424 

Concrete Base: 

Cement at $1.48 per bbl. on job, net $1 . 365 $0 . 227 

Sand at $1.40 per cLi. yd. on job.. 0.731 0.122 

Gravel at $1.50 per cu. yd. on job 0.934 0. 156 

Coal and water 0.035 0.006 

Labor 0.336 0.056 

Miscellaneous expense . 038 .017 

Total, exclusive of superintendence, depreciation on 
machinery, administration $3 . 439 $0 . 584 

The pavement was 34 feet wide. The proportions of the con- 
crete were 1 : 3 : 5; and the thickness was 6 inches. The concrete 
was mixed in a one-bag mixer. The loss on bags was 1 per cent. 
The wages of common labor was 20 cents per hour ; the engine runner 
on the concrete mixer, 30 cents per hour; and a team, wagon, and 
driver, 50 cents per hour. 

791. Old Macadam foundation. It not infrequently hap- 
. pens that a high-class pavement is to replace a water-bound gravel or 

macadam surface, in which case it may be economical to use the old 
pavement as a foundation for the new. This form of foundation has 



406 FOUNDATIONS FOR PAVEMENTS [CHAP. XV 

been discussed in connection with the construction of concrete roads. 
The possibihty of utiUzing an old gravel or macadam road as a foun- 
dation occurs more frequently with a narrow concrete or brick rural 
road than with a comparatively wide street pavement. For a con- 
sideration of the difficulties encountered and of the methods to be 
employed, see § 437. 

792. Bituminous Concrete Foundation. Bituminous- 
cement concrete has some advantages over hydraulic-cement con- 
crete for pavement foundations. 1. The bituminous concrete does 
not require any time for curing and hardening; and consequently 
the wearing coat may be laid as soon as the foundation is completed, 
which may be a decided advantage on a busy thoroughfare. 2. 
The bituminous concrete is more flexible than hydraulic concrete, 
and hence is not so likely to crack. 3. If the wearing surface of a 
pavement is made with a bituminous cement, a bituminous concrete 
foundation is advantageous, since then the whole pavement can be 
made with one kind of equipment and organization. 4. A bitumin- 
ous wearing coat will adhere better to a bituminous concrete base 
than to a hydraulic concrete base. 5. The use of a bituminous 
concrete base makes unnecessary the binder course of a sheet asphalt 
pavement; but on the other hand, with a bituminous concrete base 
it is practically impossible to remove the bituminous wearing coat 
without materially damaging the foundation. However, it is claimed 
that by the use of a surface heater (Fig. 161, page 450), repairs can 
be made in the asphalt wearing coat without damage to the bitumin- 
ous foundation. For a further discussion of a bituminous concrete 
foundation for sheet or monolithic asphalt pavements, see § 806-08. 

793. The question of economy depends upon the local prices of 
bituminous and hydraulic cement. At present the price of bitumi- 
nous cement is substantially 1 cent per pound, while that of portland 
cement is about $2.40 for 376 pounds or about 0.66 cent per pound. 
The specific gravity of bituminous cement (a paste) is about 1, while 
that of hydraulic cement paste is about 2; and hence the prices per 
unit of volume are about 1 to 1.3, or in other words, at present prices 
the hydrauUc cement concrete is about 30 per cent the more expen- 
sive. Or to put it another way, when portland. cement costs more 
than $1.88 per barrel, there is a possibility that bituminous concrete 
may be the cheaper. There has not been sufficient experience with 
bituminous concrete to determine with any considerable accuracy the 
cost of mixing and laying it. 

794. Bituminous concrete pavement foundations were used in a 



ART. 3] FOUNDATIONS OF TRACKS 407 

number of cities in this country from about 1880 to 1895, owing prob- 
ably to the high price of hydraulic cement, particularly portland 
cement; and some of these foundations are still giving satisfaction. 
Tar concrete has been used in England for pavement foundations 
for many years. 

795. The strength of a bituminous concrete foundation will 
depend upon the kind and quality of the bituminous cement used; 
and no such foundation is as strong as one made with equal care of 
Portland cement. 

Art. 3. Foundations of Street-railway Tracks 

796. One of the most common failures of pavements is adjacent 
to the rails of a street-car track; and is often due to the defective 
foundation of the track. In a general way these failures are due to 
the vertical vibrations of the rails, which pounds the foundation 
to pieces and also breaks the bond between the rail and the pave- 
ment, thus permitting water to enter which on freezing heaves the 
pavement. The vibrations of the rail may be due to the deflection of 
the rail or to the compression of the ties and foundation or to both. 

The design and usually also the construction of the foundation 
of the track is a function of the engineer of the street railway, while 
the construction and maintenance of the pavement adjoining the 
track is under the direction of the city engineer; but to secure 
reasonably satisfactory results requires the co-operation of both 
interests.* 

797. Foundation. The foundation may be of gravel, or 
broken stone or concrete. With gravel ballast it is practically 
impossible to prevent the rail from working up and down owing to 
the movement of the ballast and the difficulty of tamping the ties 
uniformly. Broken stone gives better results than gravel, but is far 
from satisfactory. Gravel or broken-stone ballast is reasonably 
satisfactory for railways in the open country upon a private right- 
of-way; but the case is very different on a city street where all have 
equal rights and which must be paved and maintained for general 
public use. It is generally conceded that the track, at least in streets 
having any considerable amount of heavy traffic, should rest upon a 
concrete foundation. 

* For an instructive article on the relations of the two interests involved and a discussion 
thereon by several engineers, see "A Suggested Change of Policy for Maintaining the Pave- 
ment adjoining the Railway," by N. S. Sprague, Chief Engineer of Bureau of Engineering, 
Pittsburgh, Pa., in Proc. Amer. Soc. Municipal Improvements, 1915, p. 271-77 and 277-82. 



408 



FOUNDATIONS FOR PAVEMENTS 



[chap. XV 



There is great variety in the form of the concrete foundation. It 
may be a slab of uniform thickness extending under the track, or the 
thickness may be increased longitudinally under each rail or trans- 
versely under each tie. An important advantage of the first form of 
construction over either of the others is that it eliminates trenches in 
the subgrade, which can not be rolled and which are hkely to be par- 
tially filled with loose earth by the breaking down of the edges of the 
trench by workmen. With the trench construction the depth of the 
concrete is not likely to be uniform, and is hkely to be laid on loose 
earth instead of a compacted subgrade. 

798. Examples. Fig. 143 shows the two types of track founda- 
tions recommended by the Committee on Way of the American 



Paving omitted^ \ f/ieighf- goyemed\ib/ /XTiz/ng 

"t'^'d"' n ! '-'*' ' . ' r- Vl'- ' ■* • y. ■ ■ ■. ■> ■ ■ .'■■»• '.. > l ■ ■ ■■.» ■ ■ ■ ■;.> •■ ■ T 



G"xQ"x6' fie 



n ^ol<^ Grave/. ander3,.or c> 



May exfenc/ /" fo3"abovey 4"fn<o 
boffom of fi'e- d^rx/zng tj/e 
on dep/h ofpat^/ng base. 




.Pfo9''of/. 3:G concrefe 






■Loarr? 

ffo/fed bo/Zasf G'. 
Pebb/es or c//?</ers 




Ora//? or? 

jik^,^ ., /• _/ . ^ ^ . cen/Br//?7e cfctoi/b/efrac/r. 

/Vways firov/de surface c/ha/ns, ond u/7der dncr/ns oo(f/' in foam or cJby. 

Typ£ 3:- fbr o// 3o/h exc^ very /jeavy c/ay, fijr chnse /n7/T/c, 
and for cars ajo /o JS /Q/ts *ye/gihf: 



Po^/^ oipijfed 



G concrefe. 




ingfbr 
it^eep/Tofe 
Loam 



\er/7e 



IfJoG'f/fe 

P^dt/es or Cf'fTders-,^ ^ ^ . 

n/wr/70ffve an7/non 
center //no of doab/e f/TTcA 
Alrvays prot^xfe surface and under cfra/ns. 

TypeC:- fbr t?^yy y^/hr-rv^/r/ri^ so// ara^a/?asr/a//7 mad^ (^rourfcf, 
for densest traff/c, arc/ for /?eat<fe'sf cars. 

Fig. 143. — Track Foundations for Paved Streets. 

Electric Railway Engineering Association.* Notice that in both 
examples the rail is the T pattern; but as far as shown in Fig. 
143, there is no difference between the T and the grooved rail. 
For track foundations with a grooved rail, see Fig. 159, page 442, 
Fig. 160, page, 443, and Fig. 196, page 540; and for two track- 



* Proceedings Amer. Elect. Ry. Eng'g Assoc, 1915, p. 471. 



ART. 3] 



FOUNDATIONS OF TRACKS 



409 



foundations with T rails, see Fig. 197, page 540. Notice that the 
lower half of the last shows a concrete beam under each rail. 

For a cross section of a street-railway track in a sheet asphalt 
pavement, see Fig. 159 and 160, page 442-43; in a brick pavement, 
see Fig. 196 and 197, page 540; and in a stone-block pavement, see 
Fig. 218, page 587. 

799. The Ties. The ties are either wood or steel, the former 
being the more common. Wood ties have a long hfe when embedded 
in concrete, especially if treated by some preservative process; 



■^'-^'Gage- 



■3'-ef- 



f ; ^4t/" Jfee/ Tie Q--9"/dnQ tV^perF/: f^.SLb ^'V:':v:: f ^V^A 

/: ■ j ■ T. ■ . ■ ■ ■ i. ■ ■ - . ! w 1 t ■ b I 1; 5 ; • t:^y 






% 

I 

Fig. 144. — Steel-tie Street-railway Track. 



•-^^ 



and there is an increasing use of treated wood ties. For illustrations 
showing track with wood ties, see Fig. 143. 

Steel ties have been used to only a comparatively small extent. 
For a cross section of the track with steel tie used in Chicago, see 
Fig. 144. The construction shown in Fig. 144 has been found 
to be objectionable on account of the difficulty of paving around 
and over the tie-rod between the rails. Concrete ties have been 
used in street-railway track only a little, if at all. 

800. THE Rails. The rails are one of three types, viz.: the 
flat-top, the grooved top, and the T section. The flat-top rail, which 
has been almost abandoned, was very destructive of the pavement, 
as steel-tired vehicles frequently ran with one wheel on one of the 
railway rails, the result being that the wheel on the pavement wore a 
rut. Where the flat-top rail is in use, it is not imcommon to find at 
least two ruts on each side of each track — one made by a broad-gage 
wagon running with its left wheels on the left rail and its right wheel 
to the right of the right rail, one made by any wagon running with its 
left wheel on the right rail; and if the wagons are of two different gages, 
the last position will cause two narrow ruts close together or one wide 
one. For illustrations of track construction using the T section, see 
Fig. 143, page 408, and Fig. 197, page 540; and for illustrations 



410 FOUNDATIONS FOR PAVEMENTS [CHAP. XV 



showing a grooved top, see Fig. 159 and 160, page 442-43, and Fig. 
196, page 540. 

801. The Paving. Tn selecting the material for the pavement 
adjacent to the rails, consideration should be given to the amount 
and character of the vehicular traffic and to the relative cost and life 
of the several classes of pavements. The preference of the members 
of the American Electric Railway Engineering Association is as 
follows: granite-block, Medina sandstone-block, creosoted wood- 
block, vitrified brick, asphalt-block, sheet asphalt, bituminous 
concrete, bituminous macadam, water-bound macadam. The rail- 
way company usually prefers granite block because of its durability, 
and possibly also because its roughness deters vehicles from using 
the railway area. 

The precautions to be taken in laying the different paving mate- 
rials adjacent to a street-railway track will be considered in the sub- 
sequent chapter treating the respective kind of pavement. 

For cross sections of a sheet asphalt pavement adjacent to a 
street railway track, see Fig. 159 and 160, page 442-43; for a cross 
section of a brick pavement and a street-railway track, see Fig. 
196 and 197, page 540. 



CHAPTER XVI 
ASPHALT PAVEMENTS 

802. For a discussion of asphalt, its sources, its characteristics, 
the methods of testing it, and specifications for asphalt for different 
purposes, see Art. 1 of Chapter VIII — Bituminous Road Materials. 

Asphalt is used in three forms of pavements, viz. : sheet asphalt, 
asphalt concrete, and asphalt block. The wearing coat of the first 
consists essentially of an asphalt mortar, i. e., a mixture of sand and 
asphalt cement; and that of the second is an asphalt concrete, i. e., 
a mixture of broken stone and asphalt cement. Both of these forms 
of asphalt pavements are mixed and laid hot. The wearing coat of 
an asphalt block pavement consists of blocks of asphalt concrete 
moulded hot and laid when cold. The first form is by far the most 
common; but the second, of which bituHthic pavement is a form, 
although a comparatively recent development, is quite widely 
used (§ 636). 

Each of >these forms will be treated in a separate article. 

Art. 1. Sheet Asphalt Pavements 

803. A sheet or monolithic asphalt pavement consists primarily 
of (1) a wearing coat IJ to 2 inches thick composed of asphalt 
paving cement mixed with sand; (2) a binder course 1 to IJ inches 




i "Aibha/r liinrBinder/in 



W^-i:^/^ 






r;>M Con crete 5/n.M 



g^jJ5i?*=7i?^w:^^5^5^«J^^537 




Fig. 145. — Two Forms op Sheet Asphalt Pavements. 



thick, composed of broken stone and asphalt cement; and (3) a 
foundation of hydrauUc-cement concrete — see Fig. 145. 

In this country when the term asphalt pavement is used the above 
form is usually intended. The term sheet or monolithic pavement is 

411 



412 ASPHALT PAVEMENTS [CHAP. XVI 

not distinctive, since rock asphalt also is laid as a continuous sheet; 
but no confusion is likely to result, since in this country the term 
sheet is commonly used to distinguish the monoHthic form from the 
asphalt-block pavement, and since in Europe only one form of asphalt 
pavement is used, monoHthic natural rock. In contra-distinction 
to a pavement made of natural asphalt Hmestone or sandstone, the 
above pavement could with some propriety be called an artificial 
asphalt pavement, or the wearing coat could with still more propriety 
be called an artificial asphalt paving compound; but the dis- 
tinction is not important, since the sheet asphalt pavement is laid 
almost exclusively in this country and the rock asphalt almost 
exclusively in Europe. 

804. Historical. The first artificial sheet asphalt pavement 
in this country was laid in Newark, N. J., in front of the city hall in 
1870. In 1873 a small piece was laid on Fifth Avenue, New York 
City, opposite the Worth Monimient. A few other experimental 
sections were laid; but the first test on a large scale was in 1876 on 
Pennsylvania Avenue, in Washington, D. C. Preceding 1882, out- 
side of Washington, D. C, there were not more than half a dozen 
streets in this country paved with any form of asphalt; but since 
that date, asphalt pavements have increased rapidly, and now hun- 
dreds of miles of it are in use on the streets of American cities. The 
following statistics show the rapid growth of this industry: In this 
country in 1880 there were 300,000 square yards of sheet asphalt 
pavements; in 1885, 1,800,000; in 1890, 8,100,000; in 1895, 21,500,- 
000; in 1900, 38,000,000; in 1909, 83,227,000. In Europe in 
1900, the latest data available, there were only about 3,000,000 
square yards of asphalt pavements of all kinds. 

In 1909 in the United States according to the data on page 320, 
about one fifth of all pavements were sheet asphalt; and if water- 
bound gravel and macadam be excluded, about one third of all 
durable pavements were sheet asphalt. 

Asphalt pavements can be adapted to a wide range of tempera- 
ture, and are in extensive use from Winnepeg to Panama — -from the 
far north to the tropics. 

805. THE FOUNDATION. For a description of the method of 
preparing the subgrade, see Art. 1 of Chapter XV, — Pavement 
Foundations. 

Since the sheet-asphalt wearing surface has little or no power in 
itself to act as a bridge, it is essential that it be placed upon a firm 
foundation; and consequently it is nearly always placed upon a bed 



ART. 1] SHEET ASPHALT PAVEMENTS 413 

of hydraulic-cement concrete, which formerly was sometimes made 
with natural cement but is now always made with portland cement. 
For heavy city traffic, the concrete is usually 6 inches thick; but 
for hght traffic, it is sometimes only 4 inches thick. For a discussion 
of the proper thickness of a portland-cement concrete foundation 
and the method of laying it, see § 773-84. 

It is necessary that the concrete be thoroughly dry before the 
asphalt mixture is laid upon it, as the generation of steam caused 
by placing the hot material upon a damp foundation will produce 
blistering and possibly disintegration of the wearing coat. This is a 
matter that needs close attention in laying an asphalt pavement. 
To dry the foundation after a rain or during damp weather, fine hot 
sand is sometimes spread over the concrete and then swept off; but 
this method is expensive and not very effective, and besides there is 
liability that enough sand will be left upon the foundation to inter- 
fere with the adhesion of the asphalt. 

806. Bituminous Concrete Foundation. It is claimed, with 
apparent justification, that asphalt pavements usually fail because 
of a defective foundation rather than because of inherent defects 
in the surface coat or of the wearing away of its materials; and some 
claim that better results would be obtained by the use of a bitumi- 
nous concrete foundation instead of a hydraulic concrete base. 

For a general discussion of a bituminous concrete base, see 
§ 792-95. 

807. It is claimed that the bituminous concrete base is superior 
to the portland-cement concrete foundation in four particulars, as 
f ollow^s : 

1. There is a lack of frictional resistance between the wearing coat 
and the portland-cement foundation, which gives rise to one of the 
most common failures of sheet asphalt pavements. The pressure and 
impact of wheels upon the surface of the pavement produce a horizon- 
tal component which causes the asphalt to creep and form waves or 
humps, which make the pavement uncomfortable in use particularly 
by automobiles, and these humps are difficult to remove. A shght 
roughening of the top of the concrete base is insufficient to resist this 
lateral movement; and an excessive roughening is harmful rather 
than otherwise, since a difference in thickness of the asphalt sheet 
causes a difference in compression and a consequent lateral move- 
ment. It is claimed that the asphalt wearing coat will unite more 
firmly with a bituminous concrete foundation than with a hydrauliq 
concrete base. 



414 ASPHALT PAVEMENTS [CHAP. XVI 

2. There is a lack of adhesion between the asphalt mixture 
and the portland-cement concrete, which gives rise to a second com- 
mon form of failure, since there is insufficient adhesion between the 
asphalt and the concrete to resist the action of water at the surface 
of contact of the two materials. If the concrete foundation is not 
very dense, water will be drawn to the top of it by capillary action; 
and the effect of water on the under side of the asphalt tends to dis- 
integrate the bond between the asphalt and the hydraulic concrete. 
Further, since the asphalt sheet prevents evaporation, the upper 
surface of a hydraulic concrete foundation is usually moist; and 
hence any frost action tends still further to destroy the bond be- 
tween the two materials. It is claimed that with equal care and 
equally suitable proportions, bituminous concrete will be more 
waterproof than hydraulic concrete; but the experience with 
bituminous concrete under modern methods of preparing, mixing 
and laying has been insufficient to establish such a conclusion. 

3. A third objection urged against a hydraulic-concrete founda- 
tion is that cracks in the asphalt sheet are caused by temperature 
and setting cracks in the foundation. This is probably true; but 
the wise remedy is to properly cure the concrete (§ 784). 

4. Another argument for the superiority of a bituminous base over 
a hydraulic one is that the former is more elastic; and hence absorbs 
the effect of the impact of traffic, and prevents the lateral flow of 
the wearing coat. This effect can not be very great; and it is of 
doubtful value, since the chief advantage of a monolithic asphalt 
wearing surface is its inherent stability. 

808. On the other hand, the portland-cement concrete base 
possesses the following points of superiority over a bituminous 
concrete base. 

1. A portland-cement concrete base is stronger, and hence will 
better distribute concentrated loads, will better bridge over soft 
spots in the subgrade, and will better resist the tendency to crack 
due to unequal settlement. 

2. Ordinarily it is cheaper. 

3. There is less difficulty in making repairs in the asphalt sur- 
face. 

809. Other Foundations. A sheet asphalt wearing surface has 
been laid on old cobble-stone, brick, and stone-block pavements; but 
with varying success. The conditions necessary for success seem 
to be: 1. The old pavement must be firm and soUd. 2. The old 
pavement must have a fairly uniform surface so that the asphalt 



ART. 1] SHEET ASPHALT PAVEMENTS 415 

coat will have a nearly uniform thickness, say not less than 1 or 1| 
inches nor more than 2 or 2 J inches. 3. The old pavement must be 
perfectly clean and absolutely dry. 4. Of course, the asphalt wearing 
course must be made of suitable material, have appropriate con- 
sistency, and be properly applied. 

Apparently, failures in laying sheet asphalt on an old pavement 
have been more common than successes. 

810. Binder Course. In the past there has been considerable 
trouble in getting an asphalt wearing coat to adhere to a hydraulic- 
cement foundation, and various expedients have been tried; but 
at present one of two methods is always employed, viz. : either 
apply an asphalt paint coat to the foundation, or lay a binder 
course. 

811. Paint Coat. A paint coat consists of an asphalt cement 
fluxed with naphtha or benzine, which is applied with a brush or 
squeegee to the portland-cement concrete. It is essential that the 
concrete shall have a fairly smooth surface; that the base shall be 
perfectly dry; that the paint coat shall be bright and glossy, but not 
sticky; and that it shall be kept clean until the wearing coat is 
applied. 

This method of construction is applicable only to a light-traflfic 
street or road where low first cost is necessary. The method has 
been used to a considerable extent by cities in California.* 

812. Kinds of Binder Course. The binder course is a layer 
about 1| inches thick of broken stone cemented together with asphal- 
tic paving cement (§ 818) and rolled in place while hot. It is often 
called simply the binder; but this is likely to cause confusion, since 
the term binder usually refers to the cementing material in a water- 
bound gravel or macadam road, or in a bituminous macadam or 
concrete, etc. 

There are two forms of binder course, the open and the closed. 
The former does not contain as much cement, i. e., is not as rich, 
as the latter; and its aggregate is not as carefully graded. The 
open binder is used to secure a cheaper pavement; and will not 
endure under medium or heavy traffic. The closed binder has 
greater inherent stability, and hence is preferable for mxcdium or 
heavy traffic. 

813. Specifications for Open Binder. Broken Stone. The broken 
stone should be clean, and have a compact texture and uniform grain. 

* California Highways, January, 1915. 



416 ASPHALT PAVEMENTS [CHAP. XVI 

For medium or heavy traffic the stone should be strong and break 
with sharp edges and corners. 

The broken stone should have the following gradation on screens 
having circular opening: ''All of the material shall pass a Ij-inch 
screen; and not more than 10 per cent, nor less than 1 per cent, 
shall be retained on a 1-inch screen; and not more than 10 per cent, 
nor less than 3 per cent, shall pass a J-inch screen."* 

814. Sand. It is not customary to use sand in an open binder; 
and it is often specified that the stone shall not contain more than a 
certain amount of fine material. However, the more fine material 
(sand or screenings) in the binder the more compact and more 
desirable it is, provided the fine material is not more than enough 
to fill the voids. But the greater the amount of fine material, the 
more the bitumen required to coat all the particles; and conse- 
quently the more expensive the binder. For the latter reason, it is 
not customary to use much fine material in an open binder; and 
usually no fine material is used except that in the stone. 

815. Asphalt Cement. The asphalt cement is of the grade 
stated in § 542. The amount of cement should be sufficient to coat 
the fragments of stone and bind them together reasonably well; and 
will depend upon the kind and gradation of the stone and the rich- 
ness desired. With trap or hard limestone graded as above, only 

3 or 4 per cent of pure bitumen is usedj and with a soft limestone 

4 or 5 per cent is common. There should not be so much cement 
that it will run off the stone, but there should be enough to give a 
bright glossy coat to the stone. 

After being rolled the surface of the binder course will be porous 
or open, and hence the name given to it. 

816. Specifications for Closed Binder. Broken Stone. The 
quality of the broken stone should be the same as for open binder 
(§ 815). 

The gradation of the broken stone should be as follows, as deter- 
mined with screens having circular openings: " 95 per cent of the 
binder aggregate shall pass a screen having circular openings equal 
to three quarters of the thickness of the binder course to be laid; 
and the smallest dimensions of the remaining 5 per cent shall not 
exceed the thickness of the binder course. The aggregate shall have 
the following composition: 20 to 50 per cent shall pass a |-inch 

* Report of Committee of the Amer. Soc. of C. E., Proc. Vol. 42 (1916), p. 1626; or page 5 
of Specifications for Sheet Asphalt Pavements of Amer. Soc. of Municipal Improvements, 
adopted October 14, 1915, 



ART. 1] SHEET ASPHALT PAVEMENTS 417 

screen and be retained on a 10-mesh screen; and 15 to 35 per cent 
shall pass a 10-mesh screen."* 

817. Sand. The chief difference between an open and a closed 
binder is the greater density and stability of the latter. A closed 
binder should contain enough screenings or sand to fill the voids in 
the coarse material; and the gradation of the coarse and fine aggre- 
gate should be such as to give a minimum percentage of voids, and 
consequently require a minimum amount of asphalt cement. Ap- 
parently not much attention has been given to the quantity or 
gradation of the fine material, i. e., sand and stone screenings, 
for the binder course; and certainly no specifications for the fine 
material have been published. The quantities in Table 38, page 
418, are from actual practice in one of the largest cities in this 
country. 

818. Asphalt Cement. The object in using a closed binder 
course is to secure maximum stability, and hence enough asphalt 
cement must be used to coat all the fragments of the aggregate 
and fill all the voids. If the aggregate contains considerable fine 
sand and dust, the stability will be greater but more asphalt cement 
will be required. With very carefully graded aggregate 3.5 per cent 
of asphalt cement will give a very stable mixture; but if the gra- 
dation is not so good 7 per cent may be required. There should be 
enough asphalt cement to give stability; but an excess may be very 
harmful, as it will likely collect in pools in the truck while being taken 
to the street and appear in spots in the binder course, from which it 
will be drawn up on a hot day into the wearing coat and soften 
it. A uniformly distributed excess is less dangerous on a light- 
traffic street than on a heavy-traffic one, since in the former the 
wearing surface is likely to lose its volatile matter and crack, while a 
rich binder will slowly enrich the wearing surface. 

The asphalt cement should be softer than that in the wearing 
coat, because the binder is more open than the wearing coat, and 
hence more of the lighter oil^ are volatilized in the mixing, and also 
because the softer cement makes a mixture less liable to rupture. 
In ordinary practice the cement for the binder has a penetration 
20 or more greater than that for the wearing coat. 

819. Amount of Bitumen in Binder. To illustrate the method 
of determining the per cent of bitumen in a particular mixture, 

* Report of Committee of the Amer. Soc. of C. E., Proc. Vol. 42 (1916), p. 1629; or Speci- 
fications for Sheet Asphalt Pavements of Amer. Soc. of Municipal Improvements, adopted 
October 14, 1915. 



418 



ASPHALT PAVEMENTS 



[chap. XVI 



assume that the composition of the asphalt cement and the binder 
course are as stated in Table 38. The pure bitumen in the bitumi- 



TABLE 38 
Composition of Binder Course 



Asphalt Cement 


Material for Binder Course 


Bitu- 


Ingredients 


Per 
Cent 


Ingredients 


Lb. 


Per 
Cent 


men IN 
Binder 


Mexican asphalt. . . 
Trinidad asphalt. . . 
Indian flux 


40 

40 
20 


Asphalt cement 


122 

438 

1 190 


7 
25 
68 




Sand. 




Broken stone 






One batch or boxful 




Total 


100 


1750 


100 


5.8% 



nous materials is as follows: Mexican asphalt, 99.6 per cent; 
Trinidad asphalt, 56.0 per cent; and Indian flux, 99.6 per cent. 
Then the bitumen in the asphalt cement is: 

Mexican asphalt 40 X 99.6 = 39.84% 

Trinidad asphalt 40 X 56.0 = 22.40% 

Indian flux : 20 X 99.6 = 19.92% 

Total Bitumen in Asphalt Cement =82. 16% 

Total Bitumen in Binder Course =82.16X7=5.8% 

It is impossible from the above computations to determine 
whether or not the stated amount of bitumen will fill the voids in 
the mineral matter. That could be determined accurately only by 
direct test, but could be determined approximately from a knowl- 
edge of the gradation of the mineral matter and a comparison of it 
with the composition of standard binder mixtures. The method of 
determining the amount of bitumen and the gradation of the mineral 
matter necessary to give a binder course of maximum stability is 
exactly the same as for the wearing course (§ 825 et seq.), and hence 
will not be discussed here. 

820. Mixing Binder Course. The aggregate and the asphalt 
cement should be heated separately, the exact temperature of each 
depending mainly upon the character of the asphalt cement. 
The cement is usually heated to a temperature between 120° C. 
(250° F.) and 177° C. (350° F.) ; and the aggregate is heated between 
107° C. (225° F.) and 177° C. (350° F.). 

The aggregate and the cement should be thoroughly mixed by 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



/419 



machinery until a homogeneous mixture is obtained in which all 
the particles of the aggregate are covered with cement. 

The mixing is done in a box in which revolves two axles each 
carrying a series of obhque paddles set spirally — see Fig. 146. 




Fig. 146. — Machine for Mixing Asphalt Binder. 



The mixture is discharged through a sliding door in the bot- 
tom of the box. The capacity of mixers vary from 1000 to 2000 
pounds. 

Fig. 147, page 420, shows a complete semi-portable asphalt mix- 
ing plant. On the left is the boiler; and on the right is the elevator 
for the fine and coarse aggregate, and the drum for drying them. 
Behind the boiler is the asphalt-heating tank or kettle; and behind 
the sand-drying drum is the mixer with sand-storage bins above it. 

Fig. 148, page 421, shows a portable asphalt-mixing plant. Sim- 
ilar plants are mounted upon one and sometimes upon two steam- 
railroad cars. In the larger cities are fixed plants which consist of 
quite a group of buildings. 

821. Laying Binder Course. The binder course should be trans- 
ported to the street in wagons or trucks covered with canvas or tar- 
pauHn; and when delivered should have a temperature between 93° 
and 163° C. (200° and 325° F.), the temperature between these 
Hmits being regulated according to the temperature of the atmosphere 
and the ease with which the binder course can be spread. The 
temperature of the binder on the street should be no greater than is 
necessary to permit the mixture to be easily spread. 

The stone should be covered with a bright glossy coat of asphalt 



420 



ASPHALT PAVEMENTS 



CHAP. XVI 




Fig. 147. — Semi-portable Asphalt Mixing Plant. 



AET. 1] 



SHEET ASPHALT PAVEMENTS 



421 



cement, as otherwise it will have no coherence. On the other hand, 
there should be no excess of cement, as is shown by its running 
from the bottom of the truck or by too great richness of the bottom 
of the load. If the stone was heated too hot, the cement may run 
off the stone at the top of the load and accumulate at the bottom, in 
which case the surface of the load will appear dull and dead. 

On arrival on the street the mixture should be dumped upon the 
foundation at such distance from where it is to be spread as to 





11 ' m:^W 


Wk^ 







Fig. 148. — Pohtable Asphalt Mixing Plant. 



require that all of the material shall be moved from v/here dumped. 
This is necessary to secure a uniform thickness after rolling, since 
the portion at the bottom of the pile is considerably compressed by 
the fall and the weight of the incumbent mass, and hence if it is not 
moved the binder course after being rolled will be thicker at this 
point than elsewhere. 

The binder is first roughly shoveled into place, and then is leveled 
off with rakes or shovels. An open binder may be leveled with hot 
iron rakes having long tines; but if a closed binder is employed, the 
spreading should be done with a shovel or the back of a rake, as the 
use of the tines will bring the larger stones to the surface and produce 



422 



ASPHALT PAVEMENTS 



[chap. XVI 



segregation. Fig. 149 shows the spreading of the binder course. 
Notice that the binder is dumped on a steel plate from which 
it is shoveled into place. 

The binder course may be allowed to cool somewhat before being 
rolled, for if it is too hot when rolled it is hkely to stick to the roller 
and also be pushed out of place. The roUing should be done with a 
self-propelled tandem roller weighing 5 to 7 tons, giving a pressure 




Fig. 149. — Spreading the Binder Course. 

of not less tnan 20U pounds per hneal inch of tread. The object of 
the rolling is a kneading action as well as a compression, and hence 
many passes of a light roller are better than a few passes of a heavy 
roller. 

After rolling the surface should be of uniform density; and par- 
ticularly there should be no spots containing an excess of asphalt 
cement, since on a hot day the excess is likely to be drawn up into 
the wearing coat and soften it. 

822. After the rolling of the binder course is completed, the 
wearing coat (§ 825) should be applied at once, while the binder is 
clean and hot ; or it should at least be added during the same day for 
fear the binder may become dirty and dusty. This is necessary to 
secure the maximum bond between the binder and the wearing coat; 
and if this is not done, the binder course should be protected from 
mud and excessive dust. 

823. Thickness of Binder Course. The proper thickness of the 



ART. 1] SHEET ASPHALT PAVEMENTS 423 

binder course depends upon the amount of the traffic. For Hght 
traffic the thickness is usually 1 inch after being rolled and for medium 
traffic is IJ inches, while for very heavy traffic it is sometimes 2 
inches. For data on the thickness of binder course in various cities, 
see Table 46, page 453. 

The compression by rolling is usually about 40 per cent. The 
area that a given weight of the binder course will cover will depend 
upon the hardness and gradation of the stone, upon the consistency 
and temperature of the asphaltic cement, and upon the degree of 
compression. 

824. The thickness to which the compressed mixture should be 
spread to give the specified thickness can be determined either by 
computation or by trial. 

1. To compute the area to be covered by a given weight, first 
determine the specific gravity of the compressed binder course, and 
then compute the area that a given weight should cover to give the 
required thickness after rolling. 

2. Lay a given weight on a known area, roll it, and then measure 
the thickness by probing at several points with a dull pointed awl, 
being careful that the awl penetrates to the foundation. After a 
few trials the exact area to be covered by a stated weight to give the 
desired thickness, can be accurately found. 

825. Wearing Coat. The wearing coat consists of sand, and 
fine mineral dust or filler, and asphalt cement. The sand and filler 
are often referred to as the mineral aggregate. 

826. The Sand. The sand is a very important element in a 
sheet asphalt pavement, since it constitutes at least three fourths 
of the wearing coat. The sand should consist of hard and durable 
grains. It shoifld be free from vegetable matter, and should not 
contain much clay or loam; although a small amount of these, if not 
closely adhering to the grains, will act as a filler and do no harm. 
However, a small amount of clayey material adhering to the grains 
is highly objectionable, since in passing through the heating drum or 
dryer it is likely to be burned onto the grains to such an extent as 
not to be removed in the mixer and consequently the bitumen will 
not adhere well to the sand. 

The gradation of the sand, i. e., the relative proportions of grains 
of different sizes, is the chief characteristic to be considered; occa= 
sionally, however, a sand is found which for some unknown reason, 
perhaps the shape of the grains or character of the surface, proves 
to be unsuitable for sheet asphalt pavements. 



424 



ASPHALT PAVEMENTS 



[chap. XVI 



827. Gradation of Sand. Until comparatively recently but little 
attention was given to the gradation of the sand; but it is now 
known that this is one of the most important elements in the 
construction of a sheet asphalt pavement. Table 39 shows the 
grading of the sand used for the wearing coat of sheet asphalt pave- 
ments in a number of cities before the importance of this element was 
appreciated. The last hne of the table shows the grading now be- 
heved to be the best attainable. The data in this table are mainly 
interesting as showing a possible reason for the unsatisfactory service 
of some sheet asphalt pavements. 



TABLE 39 

Former Grading of Sand for Sheet Asphalt Pavements* 



City. 



Boston, 1899: 

Buffalo: 

bank, fine 

lake, coarse 

Chicago, 1896: 

fine 

medium 

Louisville : 

river 

bar 

Milwaukee : 

coarse beach 

White Fish Bay.. 

Omaha 

St. Louis, 1897: 

coarse 

fine 

river, coarse 

fine 

Richardson's Ideal :t 

mineral aggregate 

sand proper 





Per 


Cent 


Passing Sieve No. 




200 


100 


80 


50 


40 


30 


20 


10 
2 


6 


13 


14 


31 


20 


10 


4 


'I 


39 
6 


21 
10 


8 
41 


1 
19 


15 


5' 


3 


10 
2 


68 
15 


15 
17 


5 
52 


2 
9 








2 


2 


1 


2 
32 


2 
2 


1 
33 

1 
25 
19 


4 
13 

2 

29 
19 


53 
18 

36 
36 
41 


25 
3 

32 

4 

12 


10 
1 

17 
3 
3 


3 


2 


9 

1 
2 


3 

'2' 




14 

2 

17 


1 
26 

4 
40 


1 
14 
22 
30 


48 
38 
28 
10 


46 

6 

19 

1 


3 
2 
10 
1* 


1 





10 
1 


5 


14.5 
0.0 


14.5 
17.0 


14.5 
17.0 


26.2 
30.0 


12.3 
13.0 


9.0 
10.0 


5.6 
8.0 


3.4 
5.0 



Total 

Per 

Cent. 



100 

100 
100 

100 
100 

100 
100 

100 
100 
100 

100 
100 
100 
100 

100 
100 



* Richardson's Modern Sheet Asphalt Pavement, p. 85. 
t Ibid., p. 332. 

The ideal grading for sand for a sheet asphalt was obtained by 
analyzing pavements that had given the best service; and has been 
abundantly tested in practice for more than twenty years. Unfor- 
tunately it is not often that a natural sand can be found which 
approximates the ideal grading; and therefore an artificial mixture 
must be prepared by screening the sand into several lots excluding 
one or more of the lots, and then remixing the remainder, or by com- 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



425 



bining portions of different sands. Unless the available natural 
sand is nearly ideal, the securing of the best grading will entail con- 
siderable expense ; and in this case it may be wiser to accept a grading 
only approximating the ideal. Table 40 shows the ideal grading for 
heavy traffic and also two permissible gradings. 



TABLE 40 

Standard Gradings for Sand for Sheet Asphalt Pavements 





Passing 
Sieve No. 


Richardson's Gradings.* 


Forrest's Per- 


Grade of 
of Sand. 


Ideal for Heavy Traffic. 


Permissible for 
Light Traffic. 


missible Grad- 
ing, t 


Dust 


200 

100 
80 

50 
40 

30 
20 
10 

8 


00.0 

17.0% 
17.0 


00.0 

26.0% 

30.0 
13.0 

43.0% 

30.0% 
0.0 
100 


00 


Fine 








Medium 


Total 34% 

30.0% 
13.0 


20 to 30% 






Coarse 


Total 43% 

10.0% 
8.0 
5.0 


not over 40% 






Very coarse 


Total 23% 

0.0 
Total 100 100 


20 to 30% 
not over 10% 




100 



♦Richardson's Asphalt Construction for Pavements and Highways, 1913, p. 29. 
t C. N. Forrest, Chief Chemist, Barber Asphalt Paving Co., in private letter to the author 
dated August 17, 1917. 

Notice that the aggregate for heavy traffic is finer than that for 
hght traffic. The reason for this is as follows: Large pieces of 
aggregate will be fractured sooner or later by the passage over them 
of heavy loads; and when this occurs there are two surfaces which 
are not cemented together. This condition permits a movement and 
a grinding action, and also allows the entrance of water; and thus 
two extremely destructive agents are set to work. 

Table 41, page 426, shows the grading of sands used recently by 
the Barber Asphalt Paving Co., in pavements in various cities. 
These data are instructive as showing the degree of agreement of the 
gradings of the best available sands with the standards stated in 



426 



ASPHALT PAVEMENTS 



[chap. XVI 



Table 40, and are also a valuable guide in selecting a sand for use 
in a pavement. 

TABLE 41 
Average Grading of Sands Recently Used in Sheet Asphalt Pavements * 



City. 



Boston 

Buffalo 

Chicago .... 
Kansas City . 
Louisville. . . 
New York . . 

Omaha 

St. Louis . . . 



Per Cent Passing Sieve No. 



Fine Sand. 



100 80 Total 



13.2 
16.7 
20.6 
26.3 
16.4 
14.6 
9.2 
20.5 



15.8 
12.5 
21.9 
19.2 
11.0 
13.3 
17.2 
19.2 



29.0 
29.3 
42.5 
45.5 
27.4 
27.9 
26.4 
39.7 



Medium Sand. 



50 40 Total 



42.0 

34.7 
43.6 
23.4 
35.6 
37.5 
51.1 
37.1 



15.8 
9.7 
6.4 
8.9 
17.8 
17.3 
7.9 
8.2 



57.8 
44.4 
50.0 
32.3 
53.4 
54.8 
59.0 
45.3 



Coarse Sand. 



30 20 10 Total 



6.6 
5.5 

2.5 
8.9 
9.6 
9.3 
5.3 
6.8 



4.0 
4.2 
2.5 
8.9 
5.5 
5.3 
5.3 
5.5 



2.6 
9.7 
2.5 
4.4 
4.1 
2.7 
4.0 
2.7 



13.2 
19.4 
7.5 
22.2 
19.2 
17.3 
14.6 
15.0 



c^ 



^5 



Richardson's Ideal 17.0 17.0 34.0 30.0 13.0 43.0 10.0 8.0 5.0 23.0 

* Compiled from Richardson's Modern Sheet Asphalt Pavement, p. 331. 

828. The Filler. The filler is fine mineral matter mixed with the 
sand to fill the voids, and thus reduce the amount of asphalt required, 
and also to make the wearing coat more waterproof and less plastic. 
Further, the use of a filler permits the use of a softer asphalt cement 
and thus makes the wearing coat less Uable to internal displacement 
in summer and less brittle in winter. 

The filler is usually either pulverized Hmestone or portland cement, 
generally the former. Portland cement is preferable for heavy traffic 
or where the asphalt surface is subject to the action of water. The 
heavier the filler per unit of volume the better, since this usually 
indicates greater density; and the denser the filler, the denser and 
more stable the wearing coat. The valuable part of the filler is 
the impalpable dust which is much finer than the particles just 
passing a 200-mesh sieve. " A good filler should contain at least 
60 per cent by weight of actual dust, and preferably 70 per cent." 

The amount of material in the wearing coat passing a 200-mesh 
sieve varies from 10 to 20 per cent, according to the grading of the 
sand, but usually from 12 to 16 — see § 835. Less filler is required 
with Trinidad asphalt than other kinds, since it naturally contains 
about 44 per cent of finely divided mineral matter. 

829. ASPHALT Cement. The method of preparing the asphalt 
cement has been described in § 530; and specifications for it are 
found in § 542. 



ART. 1] SHEET ASPHALT PAVEMENTS 427 

The amount of asphalt cement in the wearing coat should be 
sufficient to coat every particle of mineral matter and fill all the voids, 
but should not be enough to make the mixture too susceptible to 
pressure and temperature changes. If too much asphalt cement is 
used, the sand grains will be readily displaced among themselves, and 
the wearing coat will push out of place. If too little cement is used, 
the surface will crack and is liable to be displaced because of lack 
of solidity. The finer the mineral aggregate, the greater the amount 
of cement required for stability. Too much dust in the aggregate 
causes the mixture to be mushy. 

830. Amount of Cement. The amount of asphalt cement to be 
used in any particular case depends upon the gradation of the sand 
and the filler, and to some extent is a matter of judgment and experi- 
ence; but there are four tests that are guides in determining the 
best proportions of sand, filler, and cement for the wearing coat. 
These tests are the paper-pat test, the impact test, and the deter- 
mination of the density and the absorptive power of the compressed 
mixture. 

831. Paper-pat Test. This test is made as follows: Secure a 
sheet of manila paper having a smooth surface, crease it down the 
middle, and lay it opened out on a smooth firm wood surface, not 
stone or metal, which would cool the mixture too rapidly. With a 
wooden paddle having a blade 3 or 4 inches wide and about f inch 
thick, tapering to an edge, take a paddleful of the hot mixture, being 
careful to get a representative sample. Note the temperature of 
the mixture. Drop the mixture side wise from the paddle on to the 
paper, and fold the paper over the mixture. With a block of wood 
press the surface of the mixture down until it is flat, and then strike 
it five or six blows with the block until the pat is about half an inch 
thick. Open the paper, and the stain upon the paper indicates the 
amount of bitumen in the mixture. Fig. 150-53, page 428-31, show 
four progressive characteristic stains.* Fig. 150 indicates a mixture 
in which there is a considerable deficiency of bitumen. Fig. 151 a 
slight deficiency of bitumen. Fig. 152 a mixture having the proper 
amount, and Fig. 153 an excess of bitumen. 

In interpreting the character of the stain consideration must be 
given to the temperature of the sample and to the kind of asphalt. 
The sample must be taken and the stain made when the temperature 
of the mixture is such that the asphalt is quite liquid. If the mix- 

* By courtesy of D. T. Pierce, Executive Assistant, Barber Asphalt Paving Co. 



428 



ASPHALT PAVEMENTS 



[chap. XVI 




Fia. 150. — Light Stain. 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



429 



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H^BKu^Sj^^^^^^Hp^^^H^^^fl^a 


' '^^^ S^ 


^^mtBKB^^^-^ 




!'^'«^^^^|||3H8lB^al^^^ 




' "'^^t^^^O^^^KP^i^^^'' 




' *'-'^T^^^^^^^^s^M'""' 












'.»,'' •»■ 






. " - ■ 





Fia. 151. — Medium Stain. 



430 



ASPHALT PAVEMENTS 



[chap XVI 




Fig. 152. — Strong Stain. 



II 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



431 



'/ ■ 






# >~<^^£^^^^^|^^^^^^^^^^^^^^^^^|^^^^^^^^H 




'^.^^^■■^^^^^I^^H 


»' 'f^^^^^^^^^^^^H^^H 




'^^hHH[^^^^^^^^^^^^^^^^|^^^^^^^^^^^^^^^^^^^^^^^H 


^^'^^Bh^^^^^H^^^^^^^^^^^H^R 






> » , 


' '-( 



Fig. 153.— Heavt Stain. 



432 ASPHALT PAVEMENTS [CHAP. XVI 

ture is too cold, the test is of no value ; and if the mixture is too hot, 
the stain will be stronger than for the proper temperature. Further, 
the test is more valuable for Trinidad asphalt than for other kinds of 
asphalt, since the latter are more susceptible to temperature changes. 

The appearance of the surface of the hot pat is nearly as instruc- 
tive as that of the stain on the paper. If the mixture is unbalanced 
in any way, the surface will have a greasy appearance, which may 
be due to an excess of either bitumen or filler; but the cause of the 
greasiness can be determined only by trial. 

832. Density. Another method of testing the correctness of the 
proportions of the wearing coat is to determine the density, or spe- 
cific gravity, of the compressed mixture. A cylindrical test speci- 
men IJ inch in diameter and about 1 inch high, is moulded while hot 
under standard pressure. The specific gravity of the specimen is 
then determined either by weighing it in air and in water, or by 
weighing it in air and measuring its volume. 

The following example illustrates the method of making this test.* 

The customary mixture in parts by weight is : 

Sand 75 per cent 

Dust or filler 10 '' " 

Trinidad asphalt cement 15 " " 

Total 100 " " 

The specific gravity of the sand is 2.65, the limestone dust 2.60, 
and the asphalt cement 1.25. The volumes of the materials in the 
mixture are : 

Sand '. 75 -^ 2 . 65 = 28 . 30 units of volume = 64.10% 

Limestone dust 10-2.60=3.85 '' '' " = 8.72 

Asphalt cement 15^1.25 = 12.00 " " " =27.18 

Total 44.15 " " " =100.00% 

If the mass is compressed so as to exclude all the entrained air, 
i. e., so that all the voids in the mineral aggregate are filled with 
asphalt cement, then the specific gravity of the mixture would be: 

Sand 64.1% X 2.66 = 1.699 

Limestonedust 8.7% X 2.60= .226 

Asphalt cement 27.2% X 1.25= .340 

Ultimate specific gravity = 2 . 265 

The specific gravity of the specimen should be at least 2.20, and 
is usually not over 2.22. If portland cement is used as a filler instead 
of limestone dust, the specific gravity will be about 0.02 higher, 

=«' Richardsoa's Modern Asphalt Pavement, p. 581. 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



433 



since the specific gravity of portland cement is about 3.10. The 
greater the proportion of asphalt, the less the specific gTSLvity. 

If the specific gravity of the specimen is 2.22, the voids are: 
(2.265 - 2.22) -^ 2.265 = 2 per cent. 

Pavements having the standard grading, after being rolled, have 
within 1 or 2 per cent of the ultimate specific gravity; but some 
pavements laid without regard to the best gradation, have specific 
gravities as low as 1.90, and have not given reasonably satisfactory 
service. 

833. Absorptive Power. The denser the mixture and the larger 
the percentage of bitumen it contains, the more resistant it will be 
to the action of water ; hence a determination of the absorptive power 
of the compressed mixture gives valuable information concerning 
the correctness of the proposed proportions, particularly if the pave- 
ment is to be laid in a humid atmosphere. 

The absorptive power is determined by moulding a cylindrical 
specimen as in determining the density (§ 832), weighing it, suspend- 
ing it in waterj and then weighing it at intervals. The gain in 
weight is the water absorbed; and the absorption per unit of area 
may then be computed. Table 42 shows the results with two mix- 
tures, the first containing coarse sand and too little filler, and the 
second being Richardson's ideal mixture. 

TABLE 42 

Absorption of Cylinders op Wearing Coat * 

Pounds per Square Yard 



Interval 



Seven days 

Fourteen days . . . . 
Twenty-eight days. 



Washington Mixture, 
1893 



Trinidad 
Asphalt. 



0.314 
0.434 
0.502 



Bermudez 
Asphalt. 



0.063 
0.194 
0.306 



Ideal Mixture, 1904. 



Trinidad 
Asphalt. 



0.080 
0.093 
0.107 



Bermudez 
Asphalt. 



0.094 
0.093 
0.104 



834. Impact Test. A cylindrical test piece is moulded as in 
making the density test (§ 832), and then it is subjected to suc- 
cessive blows of the dropping weight of the impact machine, f The 
dropping weight or hammer weighs 2 kilograms (4.40 lb.); and the 
height of fall is 1 centimeter for the first blow, and an increase of 1 
centimeter for each successive blow until the test piece fails. The 



* Richardson's Modern Asphalt Pavements, p. 468. 

t Bulletin No. 44, Office of Public Roads, U. S. Department of Agriculture, June 10, 1912, 
p. 9-11. 



434 



ASPHALT PAVEMENTS 



[chap XVI 



number of blows required to produce rupture is assumed to repre- 
sent the toughness of the specimen. The number of blows required 
to produce failure will depend upon the consistency of the asphalt 
cement and upon the temperature of the specimen at the time of 
testing. The best mixtures at a temperature of 78° F. require from 
20 to 30 blows to produce rupture. 

835. Proportion from Practice. Table 43 shows the grading of 
the wearing coat of sheet asphalt pavements laid in 1916 and 1917 
by different contractors in a number of cities,* and also Richard- 
son's ideal proportions! and Forrest's permissible composition.! 



TABLE 43 

Proportions for Sheet Asphalt Pavements 

Laid in 1916 and 1917 



Ref. 
No. 



Locality. 



State. 



Massachusetts. . 



New York 

North Carolina. . 
Ohio 



South CaroHna. 



City. 



Boston. . . 
Roxbury. . 
New York 
Kingston. 
Hannilton. 
Newark . . 
Sumter. . . 



Richardson's Ideal, at least. 
Forrest's Permissible 



Bitu- 
men, 



per 
Cent. 



11.4 
10.1 
10.4 
10.5 
10.2 
10.1 
10.0 

10.0 
9-11 



Per Cent Passing Sieve No. 



200 100 



12.6 
12.9 
17.1 
11.6 
16.1 
10.3 
11.0 

10.0 
10-12 



17.0 7.0 
12.0 6.0 

13.6 
9.4 7.4 



7.7 
14.2 
13.0 



3.9 
16.2 
10.0 



10.0 20.0 
15-25 



50 40 30 20 10 



21.0 10.0 

17.0 11.0 

47.0 



30.7 
18.9 
30.9 
25.0 



10.1 

12.1 

4.3 

12.0 



24.0 10.0 

least 
possible 



5.0 
9.0 

12.3 
5.9 

10.4 
3.1 
7.0 



3.0 5.0 
15-25 



6.0 
10.0 



7.6 
5.8 
5.1 
2.0 

3.0 



2.0 

1.0 
1.5 
1.5 
1.8 
2 9 



836. The specifications for sheet asphalt pavements adopted 
by the American Society of Municipal Improvements on October 14, 
1915, contain the following requirements for the composition of the 
wearing coat: 

Bitumen 9.5 to 13.5% 

Passing 200 mesh not less than 10% } ^^^^^ ^^^ ^^^^ ^^^^ 25% 

total 15 to 50% 



80 mesh 10 to 35% 

50 mesh 4 to 35% 

40 mesh 4 to 25% 

30 mesh 4 to 20% 

20 mesh '. 4 to 12% 

10 mesh 2 to 8% ^ 

8 mesh to 5% 

minimum amount of bitumen shall be used only in mixtures 



total 10 to 35% 



Passing 
Passing 
Passing 
Passing 
Passing 
Passing 
Passing 

" The 

taining the minimum passing the 80 mesh; and the percentage of bitumen 

must increase as the amount passing the 80 mesh increases." 

* By courtesy of D. T. Pierce, Executive Assistant, Barber Asphalt Paving Co., in letter to 
the author under date of ^lept. 14, 1917. 

t Richardson's Modern Sheet Asphalt Pavement, p. 326. 

t C. N. Forrest, Chief Chemist, Barber Asphalt Paving Co., in letter to 'the author dated 
August 17, 1917. 



con- 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



435 



837. Percentage of Bitumen. Notice that Table 43 shows the 
percentage of bitumen ; while the wearing coat is a mixture of asphalt 
cement, filler and sand. To compute the percentage of bitumen 
in the wearing coat proceed as follows: Assume that the asphalt 
cement and the wearing coat have the compositions stated in 
Table 44. 



TABLE 44 
Composition of Wearing Coat 



Asphalt Cement 


Wearing Coat 


Ingredients 


Per 

Cent. 


Ingredients 


Lb. 


Per Cent. 


Mexican asphalt 

Trinidad asphalt 

Indian flux 


40 
40 
20 


Asphalt cement 

Limestone dust 

Sand. 


285 

300 

1415 


14.2 
15.0 

70 8 




Total 




Total 


100 


2 000 


100.0 







The bitumen in the bituminous materials is as follows: Mexican 
asphalt, 99.6 per cent; Trinidad asphalt, 56.0 per cent; and Indian 
flux, 99.6 per cent. Then the pure bitumen in the asphaltic cement 
may be computed as follows: 

Mexican asphalt 40 X 99.6 = 39.84 per cent 

Trinidad asphalt 40 X 56.0 = 22.40 " " 

Indian flux 20 X 99.6 = 19.92 " " 

Total bitumen in asphalt cement =82. 16 

Hence the total bitumen in the wearing coat is 82.16X14.02 = 11.7 
per cent. 

838. Mixing the Wearing Coat. The sand and the asphalt 
cement should be heated separately. The sand should have a tem- 
perature between 275 and 400° F. (135-205° C), and the asphalt 
cement from 250 to 350° F. (121-177° C). The exact tempera- 
ture in any case depends upon the asphalt used ; and the temper- 
ature between these limits is to be adopted to suit the particular 
asphalt. A temperature which is appropriate for one asphalt 
may harden another too much; or a temperature which makes one 
asphalt so fluid that it separates from the aggregate, may make an- 
other asphalt so stiff that it can not be properly spread and rolled. 
The sand, filler and asphalt cement for each batch or mixerful should 
be carefully and separately weighed, and then be dumped into the 
mixer. 



436 ASPHALT PAVEMENTS [CHAP. XVI 

The mixing is done in a machine hke that shown in Fig. 146, 
page 419. The mixing should be very thorough, and be continued 
until the mass is homogeneous and each particle of aggregate is 
covered with asphalt. The mixing usually requires 1 to IJ minutes. 

839. Laying the Wearing Coat. The mixture for the wearing 
coat should be brought to the street in wagons or trucks covered 
with canvas, at a temperature of 230 to 350° F. (110-177° C). 
The temperature within the above Hmits is regulated according to 
the kind of asphalt, the temperature of the air, and the ease with 
which the mixture is spread. 

The top of the binding course should be perfectly dry when 
the wearing coat is laid, to prevent the top course from being sep- 
arated from the course below by the formation of steam. Asphalt 
should not be laid in cold weather, since the paving mixture may 
become chilled between the mixing plant and the street, and par- 
ticularly when it comes in contact with the cold foundation. 

The mixture should be dumped outside of the area on which 
it is to be spread, so that it shall all be moved in being put into 
place and thus secure an even distribution of the material. This is 
very important, since great care must be exercised to prevent de- 
pressions or elevations in the finished surfaces, as the impact due to 
such spots is Hkely to cause the wearing coat to be pushed out of 
place. The mixture is thrown into place with hot shovels after 
which it is uniformly spread with hot rakes. The depth to which 
the mixture is to be spread is regulated by chalk lines on the curb, 
by the length of the teeth of the rake, and sometimes by rods sup- 
ported on feet of a length sufficient to bring the top of the rod to 
the level of the uncompacted mixture. The compression in rolling 
varies with the richness of the mixture, the leaner mixtures compress- 
ing most; and is usually from three tenths to four tenths. 

Fig. 154 shows the spreading of the wearing course of a pave- 
ment on Fifth Avenue, New York City. 

840. Immediately after being spread the wearing coat should 
be composed by rolling or tamping. Tamping irons are used 
around man-hole covers, near curbs, etc., where the roller can 
not conveniently be used. Fig. 155 shows two forms of asphalt 
tampers. The left-hand one is 8 inches in diameter and weighs 
about 30 lb.; and the right-hand one has a face 2|X5 inches and 
weighs about 18 lb. Hot smoothing irons. Fig. 156, page 438, are 
employed to finish the gutters, angles, edges, and all joints or junc- 
tures where one day's work joins that of another. The tampers 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



437 



and smoothing irons are heated in a metal basket which is moved 
forward on wheels. 

Formerly the first rolling was done with a light hand roller with 




Fig. 154. — Spheadinq the Wearing Coat of an Asphalt Pavement. 

a very long handle. Fig. 157, page 438, shows a form of hand roller 
formerly used. The hand roller has been abandoned in favor of a 
light self-propelling tandem roller (Fig. 71, page 213). The use of 





Fig. 155. — Tampers for Asphalt Pavements. 

hot smoothing irons and hot rollers are objectionable since it is 
impossible always to have them of such a temperature as not to injure 
the pavement; and since, if the mixture is delivered at the proper 



438 



ASPHALT PAVEMENTS 



[chap. XVI 



temperature, and the raking and spreading is done expeditiously, 
they are unnecessary. Experience shows that the surface of pave- 
ments upon which hot smoothing irons were used scales and flakes 
off more than a surface laid without hot tools. 




Fig. 156. — Asphalt Smoothing Ikons. 




Fig. 157. — Hand Asphalt-roller with Fire Pot. 



841. Rolling. Immediately after being spread the wearing coat 
should be rolled. It is important that the rolling should closely 
follow the spreading, so that the material shall not cool before the 
final compression is obtained. The state of the weather is an ele- 
ment to be considered; for if a strong wind be blowing, the material, 



ART. 1] SHEET ASPHALT PAVEMENTS 439 

spread over a broad surface only 2 or 3 inches thick, will cool much 
more rapidly than on a calm day when the temperature is consid- 
erably lower. 

It is usually specified that the rolling shall be finished with a 
roller giving a compression of at least 200 lb. per lineal inch. But 
to secure the best results the rolling should be begun with a 2|-ton 
tandem roller, and be followed with a 5-ton roller, and be com- 
pleted with an 8-ton roller. The first gives a compression of about 
60 lb. per linear inch of face under the front roll and about 125 under 
the driving drum; the second 200, and the third 280, under the 
driving drum. Usually only a 5-ton and an 8-ton roller are used, 
and sometimes only an 8- or 10-ton. The attempts to do all the roll- 
ing with a single 8- or 10-ton roller is very objectionable, since the 
roller is too heavy for the hot material, and hence the rolling is 
delayed until the mixture is too cold to compact well. Further, 
the maximum compression can not be produced by pressure alone, 
but requires somewhat of a kneading action; and hence several 
passages of a light roller are better than fewer passages of a heavier 
roller. On the other hand, the heavier roller is needed at the end 
of the rolling to secure the greatest possible compression. Many 
loaded-wagon tires give a greater pressure per inch of face than the 
heaviest asphalt roller; and therefore if the rolling is not done with 
a reasonably heavy roller and is not long continued, the traffic may 
make indentations on the surface and possibly seriously push the 
wearing coat out of place. 

The lubricating effect of the warm asphalt aids in the com- 
pression, so that under the roller the grains of sand are wedged 
together and the finer particles worked into the voids, until the mix- 
ture occupies less space than the mineral aggregate alone could pos- 
sibly be made to occupy. This is proved byHhe fact that if all the 
bitumen be extracted from a fragment of good pavement of known 
volume, it is found to be quite impossible to reduce the dry sand 
obtained to as small a volume as it occupied in the pavement. 

If the asphalt mixture adheres to the roller, the face of the roller 
may be shghtly moistened with a mixture of kerosene and water. 
Sometimes water is sprayed on the roller; but the use of an excessive 
amount of water should not be allowed. The sticking can be pre- 
vented by sprinkhng or dusting portland cement on the pavement. 

If the street is wide enough, the pavement should be rolled 
transversely as well as longitudinally; and if this is not possible, the 
roller should run as obhquely as possible, so that any httle inequality 



440 



ASPHALT PAVEMENTS 



CHAP. XVI 



which might be caused by the roller*s moving lengthwise may be 
taken out by the cross action. The roUing should be kept up until 
the heaviest roller leaves no mark, a result which usually requires 
at least 5 hours for each one thousand square yards of surface. 

New York City specifies that the rolling shall be continued until 
the wearing coat has a stated specific gravity, viz., 2.10 for a pave- 
ment laid between April 1st and December 1st, and not less than 
2.05 for a pavement laid between December 1 and April 1. For 
data on laboratory tests of density, see § 832. 

As soon as the rolling is completed, the pavement may be thrown 
open. Traffic, if not of too heavy vehicles, is an advantage to a newly 
laid asphalt pavement, since the pressure of the wheels aids in con- 
solidating the wearing coat and in closing the surface, a result which 
helps to retain the volatile oils and prevents the entrance of water. 
Asphalt pavements in unfrequented streets do not wear so well as 
those under a moderately heavy traffic. 

Fig. 158 shows two rollers rolling the wearing surface of an 
asphalt pavement on Fifth Avenue, New York City. 




FiQ. 158. — Rolling tee Weaeing Coat of an Asphalt Pavement. 



842. In spreading and raking the wearing coat there is a ten- 
dency for the workmen to step on the uncompressed mixture. If 
the foot-print is filled by raking material into it, this part will con- 



ART. 1] SHEET ASPHALT PAVEMENTS 441 

tain more material, and hence when rolled it will not be brought down 
even with the adjoining portion and a hump in the finished pavement 
will result. The bump of passing wheels against this hump and the 
impact due to the drop of the wheel after having passed the hump 
are nearly certain to cause a gradually increasing movement of the 
wearing coat. Therefore stepping on the uncompressed wearing 
coat should be absolutely prohibited; and if it does take place, the 
foot-print should be thoroughly obUterated by raking or at least the 
track should not be filled with loose material. 

For much the same reasons as in the preceding paragraph, all 
compressed lumps of the wearing coat should be broken up with the 
rake. Lumps in the uncompressed material make humps in the 
finished surface; and the rebound of wheels in passing such humps 
causes displacements of the wearing coat and starts waves. 

843. Thickness of Wearing Coat. The wearing coat is usually 
IJ or 2 inches thick, the former for light traffic and the latter for 
heavy. It has been estabhshed that if the wearing coat is more than 
2 inches thick, there is danger of its flowing imder travel, i. e., work- 
ing into humps and waves. 

For data on the thickness employed in various cities, see Table 46, 
page 453. 

844. The area that should be covered by a given weight of mate- 
rial can be determined in either of the two methods described for 
laying the binder course — see § 824. The method of determining 
the area by computation is more appropriate for the wearing coat 
than for the binder course, since often the specific gravity of the 
former is determined in fixing proper proportions of the ingredients, 
and also since the specific gravity of the wearing coat is not likely to 
vary as much as that of the binder course. 

If the thickness of the wearing coat is determined by probing, 
the test should be made with a putty knife rather than an awl, as in 
probing the binder course, so that the knife edge will be arrested by 
the stones of the binder course. 

845. Some engineers specify that when completed the top of 
the wearing coat shall be J inch above the top surface of the gutter 
flag, to allow for further compression by traffic without bringing the 
surface of the asphalt below the top of the gutter flag. This is of 
doubtful wisdom, since it constructs a shoulder to eliminate the pos- 
sibihty of one being formed by travel. 

846. Asphalt Adjacent to Track, It is difficult to lay and 
maintain sheet asphalt next to the rails of a street-car track. It is 



442 



ASPHALT PAVEMENTS 



CHAP. XVI 



well known that many more failures of pavements occur on streets 
having car tracks than on those without tracks, and that most of 
these failures are adjacent and parallel to the rails. Part of the dif- 
ficulties is due to the foundation, the ties, and the rails; and these 
have already been considered in Art. 3 of Chapter XV — Foundations 
of Street-Railway Tracks. Part of the difficulties with sheet asphalt 
is in getting a good union between the asphalt and the rail. The 
hot asphalt should be compressed thoroughly under and around the 
head and flange of the rail; and a good union can not be obtained if 
the rail is cold, since the asphalt will become chilled, and then can 
not be compressed and will not adhere to the rail. The surface of 
the asphalt should be laid even with the top of the rail. If it is laid 
lower, the rail will be an obstruction to vehicular travel, and vehicle 
wheels will follow the rail and make a rut next to the rail; and if 
the surface of the asphalt is laid higher than the top of the rail, 
steel-tired wheels will break down the edge of the pavement. 

Fig. 159 shows the method of laying sheet asphalt adjacent 
to railroad rails adopted in Hartford, Conn.* 

Notice in Fig. 159 that the asphalt is in contact with the rail. 
It is troublesome to maintain the connection between the rail and 
the asphalt because the deflection of the rail wifl break the bond 




Fig. 159, — Standard Practice in Hartford, Conn. 

and permit water to penetrate to the open binder where it freezes 
and lifts the wearing coat, and this allows the process to be repeated 
upon a larger scale. The only preventive is to apply a thick 
coat of soft or rather elastic asphaltic cement to the sides of the rail 
before laying either the binder course or the wearing coat; and after 
the pavement is in service, the only remedy is to fill the crack adja- 
cent to the rail frequently during freezing weather. 

Notice that Fig. 159 is for a grooved rail; but the same form of 
construction would apply equaUy well with a T rail. 



* Engineering News, Vol. 73 (1915), p. 888. 



ART. 1] SHEET ASPHALT PAVEMENTS 443 

The Baltimore (Md.) Pavement Commission has recently 
adopted the method of laying sheet asphalt pavements adjacent 
to street-railway tracks shown in Fig. 160.* Notice that a vitri- 
fied paving block intervenes between the asphalt and the rail. 
The advantage of this construction is that the vitrified blocks can 
be put into place before the laying of the asphalt is begun. The 
extreme form of the construction shown in Fig. 160 is that in which 
the whole area between the ends of the ties is paved with vitrified 
blocks — see Fig. 196, page 540, which also is a standard in Balti- 
more. 




Fig. 160. — Standard Practice in Baltimore, Md. 

847. Causes of Failure. The construction of an asphalt 
pavement involves greater care in selecting and combining the in- 
gredients than most other kinds of pavements. Most other forms 
of pavements are constructed of a natural or artificial surfacing 
material which is prepared and inspected (at least in part) before 
being brought on to the street and which needs only to be laid, while 
the important parts of a sheet asphalt pavement must be fabricated 
in place on the street; and hence greater care is required in the 
laying. 

Unfortunately the custom has been to contract with asphalt 
paving companies to lay asphalt pavements and to guarantee them 
for a term of years, and consequently the municipalities have as a 
rule made little or no investigation of the materials used nor of the 
methods employed in laying the pavement. The result is that there 
are but few, if any, public records showing the history of the pave- 
ment; and therefore it is often impossible to determine the cause 
of either failure or success. The causes of failure, exclusive of those 
due to faulty foundation and street-railway track, may be grouped 
under the following heads. Unsuitable material, improper manip- 
ulation, and deterioration in use. 

848. Unsuitable Material. The sand should be clean, hard, 
and properly graded; the filler should be hard and properly graded; 

* Engineering News, Vol. 73 (1915), p. 884. 



444 ASPHALT PAVEMENTS [CHAP. XVI 

the asphalt cement should meet the usual specifications, particularly 
as to consistency or penetration. Each of these items has already 
been discussed; and the best means of preventing failure under 
this head is to observe the standard specifications. 

849. Improper Manipulation. Even though the materials may 
be the best, there is an abundant opportunity for failure through 
improper manipulation in heating and mixing the materials. 

850. Burned Asphalt. The asphalt may have been damaged by 
over-heating or " burning.'^ The burning of the asphalt causes the 
surface of the pavement to disintegrate in spots during cold weather; 
and may be revealed by a brittleness and a tendency to crack while 
being rolled. Excessive heat converts the petroline, or cementi- 
tious constituent of asphalt, into asphaltine, which is devoid of 
cementing properties, and by so much reduces the cementing quality 
— the vital element — of the asphalt. This over-heating may take 
place during the refining (§ 492), or during the fluxing (§ 530), or 
in mixing the asphaltic cement and the sand (§ 838). 

Sometimes the kettle is mounted within brick walls directly 
over a fire which comes in contact with only a comparatively small 
part of the heating surface, in which case it is highly improbable that 
the firing will be done so evenly and slowly as not to burn at least 
part of the asphalt. The fire should not be allowed to come in 
direct contact with the melting kettle or tank, thereby guaranteeing 
that no portion of the asphalt can be burned. 'V^Hien the asphalt has 
been badly burned, it will be revealed by a brittleness during rolling; 
but there is no way of determining a lesser degree of burning, although 
it still may be sufficient to cause a serious defect which will finally 
develop into cracks and rotten spots. Therefore the inspector 
should insist upon a method of melting that will insure an unburned 
product. It is usually specified that the asphalt shall be heated 
by steam. 

The over-heating of the asphalt may be produced also by over- 
heating the sand (§ 838). Every precaution should be used to 
have each batch of sand heated uniformly throughout, and its 
temperature should be taken before mixing it with the asphalt. 
As a further check, the temperature of each load of paving 
compound sent to the street should be taken and recorded at the 
mixing plant. 

851. Improper Consistency. The paving cement may have been 
mixed too hard or too soft. If the cement is too hard, the pave- 
ment will have a tendency to crack during cold weather; and if it 



ART. l] SHEET ASPHALT PAVEMENTS 445 



is too soft, it will push out of place and form rolls or waves under 
traffic. 

852. Insufficient Bitumen. The wearing coat may not have 
contained sufficient cementing material (§ 830). Within me limits 
imposed by the proper softness and haraness of the pavement, the 
greater the per cent of asphalt the greater the life of the pavement; 
and consequently contractors in laying a pavement under a long- 
time guarantee generally use the maximum amount of asphaltic 
cement, but when the maintenance period is short they generally use 
the minimum. In fluxing, the tendency is for the bitumen to rise 
and the mineral impurities to settle; and consequently if the tank is 
worked too low, there is a likelihood that the last material taken 
from the tank will contain too small a proportion of bitumen and 
too large a proportion of sediment or mineral matter. This can be 
prevented by careful inspection and by frequently taking samples 
and analyzing them. 

853. Inadequate Mixing. The ingredients of the wearing coat 
may not have been sufficiently mixed. It is important that each 
grain of sand shall be entirely surrounded b}^ the cementing mate- 
rial, so that no two pieces shall come into actual contact. If the 
mixing is not well done, the pavement will disintegrate in spots. 

854. Rich Binder. If an excess of asphalt is used in the binder 
course, it is hkely to work to the surface of that course and then 
being absorbed by the wearing coat cause it to disintegrate. This 
cause of failure manifests itself by irregular blotches on the surface 
of the pavement. 

855. Cement Chilled. The mixture for the wearing coat may 
become chilled while being transported from the mixing plant to the 
street. To prevent this possibility, the temperature of each load 
should be taken just before it is laid. The material may also become 
chilled by a delay in tamping and rolling, or by attempting to work 
during too cold weather or during the prevalence of a high wind. 
A batch of chilled mixture will cause a weak spot in the pavement. 

856. Separation of Cement and Sand. If the distance from the 
plant to the street is long or there is unusual delay, some of the 
asphaltic cement may work down to the bottom of the load, and 
when the material is dumped there will be both rich and lean spots 
— both of which are equally objectionable. The rich spots will 
have a tendency to roll or crowd toward the gutter; and the lean 
spots will have a tendency to disintegrate under traffic. 

857. Damp or Dirtij Foundation. The wearing coat may have 



446 ASPHALT PAVEMENTS [CHAP. XVI 

been laid on a dirty or damp foundation, and therefore have been 
prevented from uniting firmly with the foundation. This con- 
dition will be revealed by a tendency of the pavement to roll or push 
out of place while sound and firm on the surface. 

858. Inadequate Compression. The wearing coat may not have 
received sufficient compression. The surface must be thoroughly 
compacted — particularly in the gutters — to keep out rain water 
and the acids and oxygen dissolved in it. The effect of oxidation 
is gradually to destroy the cementing power of the bitumen. 

859. Deterioration in Service. All materials in nature are under- 
going changes due to the action of the elements, and asphalt pave- 
ments are no exception. The following are some of the principal 
causes leading to the gradual deterioration of such pavements. 

860. Ordinary Wear. The pavement may decrease in thickness 
due to loss of material by the abrasion of hoofs and wheels; but 
since the surface is smooth and somewhat elastic, the loss by wear 
is almost imperceptible. In some cases the pavement decreases in 
thickness with use, but the decrease is due to consohdation rather 
than to loss of material. 

861. Natural Decay. All asphalts gradually lose their cement- 
ing power with age by volatihzation, evaporation, and oxidation. 
The pavement is peculiarly exposed to the action of the sun's heat, 
and to the combined action of rain water, acids, oxygen, and frost. 
The greater the cementing power of the asphalt originally and the 
softer the cement, the longer the pavement will resist the influence 
of volatilization and evaporation; and the more nearly the voids of 
the sand are filled with cement and the more firmly the pavement 
is consolidated, the longer it will resist the action of water, acids, 
oxygen, and frost. The general decay of the asphalt will be indi- 
cated by a tendency of cracks to form during cold weather (§ 866), 
particularly during a sudden and extreme drop in the temperature. 

862. Weak Foundation. A weak or improperly prepared founda- 
tion by unequal settlement or settlement in spots will cause cracks 
and depressions in the surface which under traffic will speedily enlarge 
and cause the pavement soon to break up. 

863. Porous Foundation. A porous foundation permits the 
ground water to rise, by capillary action and possibly also by hydro- 
static pressure, to the underside of the wearing coat, where by 
freezing it may break the bond between the top layer and the base, 
and thus permit the wearing coat to be pushed out of place and 
broken. This effect has been known to occur with a concrete foun- 



ART. 1] SHEET ASPHALT PAVEMENTS 447 

dation; but it is not likely to occur with good concrete. If a section 
of pavement disintegrating from this cause be examined, there will 
be found a layer of perfectly sound and good material at the surface, 
while the lower side of the wearing coat will show evidence of being 
disintegrated by water — that is, the sand will appear clean and 
white in spots as though there had been insufficient asphalt cement 
to cover it. The concrete base under the affected spot will generally 
be found to be damp or even wet. This defect may be prevented 
by underdraining the soil. 

864. Leaky Joints. Lack of a water-tight joint between the 
asphalt surface and the curb, the gutter, man-hole covers, crossings, 
street-car rails, etc., may permit the water to enter the lower and 
less compact part of the wearing coat, where by its solvent action 
and also by freezing it may do material damage. It is nearly impos- 
sible to keep these joints tight, particularly adjacent to the street- 
car rails. The damage often extends a considerable distance from 
the place where the water enters. 

865. Illuminating Gas. Ordinary illuminating gas, escaping 
from leaky pipes under the pavement, is absorbed by the pavement, 
and causes the disintegration of the asphalt. There is but one way 
to stop the disintegration of a pavement from this cause, and that is 
to stop the leak of gas. 

Pavements affected by illuminating gas first give signs of their 
disintegration by a slight depression over the affected spot, later 
fine cracks appear parallel to the line of the street, and finally the 
surface coat begins to crown. 

866. Cracks. Long irregular cracks in the wearing surface 
frequently occur during cold weather. They usually start at the 
gutter or man-hole frame, and gradually extend across the street. 
They are often found at the joint between an old and a new pave- 
ment or at the joint made between one day's work and another. 
These cracks are due to the contraction of the wearing surface, and 
should not be confounded with cracks due to the failure of the 
foundation. Usually these cracks do not occur until the pavement 
is two or three years old; at least they are most likety to occur in 
an old pavement — one in which the asphalt has lost part of its 
cementing power by age. These cracks appear sooner and increase 
more rapidly on a street having only a light traffic. When the 
pavement is subjected to a continuous traffic, the asphalt surface 
which is more or less plastic at all temperatures, is kept from crack- 
ing by the constant kneading action of the traffic. Again, when an 



448 ASPHALT PAVEMENTS [CHAP. XVI 

asphalt surface has but little or no traffic, it becomes more porous 
owing to expansion and contraction from heat and cold without the 
compression due to traffic, and as a consequence is materially weak- 
ened. If cracks occur on a street having a fair amount of traffic, 
it is evident that the paving mixture is at fault — either there was 
not enough bitumen or the asphalt cement was too hard. 

Some engineers leave expansion joints, i. e., cut the wearing 
coat through, at intervals to prevent these irregular contraction 
cracks. Such a procedure is of doubtful propriety, since the pave- 
ment if properly constructed will not crack in several years under 
the most adverse conditions, and then only at long intervals and 
generally at some old joint; and if the pavement is improperly 
made, the expansion joint will have only a sUght tendency to pre- 
vent these irregular cracks. The principle of the expansion joint is 
not applicable to materials with no structural strength, like asphalt 
mixtures. These joints are not only useless, but really detrimental 
to a pavement. They are only another form of the defect they are 
intended to remedy, for they are crevices which retain mud and 
water which tend to rot the asphalt, and the edges of the joints are 
easily broken down by traffic which also widens the crack. 

867. Shifting under Traffic. The surface coat sometimes flows 
under traffic, i. e., pushes lengthwise of the street into waves or 
crowds toward the gutter. This defect occurs in pavements having 
too soft a wearing surface, or where there is a defective bond either 
between the base and the binder, or between the binder and the 
wearing surface. This is a defect that is impossible to guard against 
entirely on a street having very heavy traffic, and especially where 
the traffic is confined to a narrow section of the street; but this 
defect is inexcusable on streets having only moderately heavy traffic. 
This flowing is commonly caused by the surface of the hydraulic 
concrete base under the pavement being too smooth, which is the 
case where gravel concrete is used or where a stone-and-gravel con- 
crete is so rich that its surface is covered with mortar that was 
brought to the top by ramming. Unless the binder and the surface 
mixtures are made very hard, a condition which makes the pave- 
ment likely to crack, the wearing coat will sHde on such a base if 
there is much traffic. Pavements often rofl from a defect in the 
binder — either because it was too rich in asphaltic cement, or becauc-e 
it was dirty when the wearing surface was laid. 

868. Damage hy Bonfires. Another cause of damage to asphalt 
pavements is the building of fires upon them. Of course this ougl. t 



ART. 1] SHEET ASPHALT PAVEMENTS 449 

never to occur, but even in the best regulated municipalities it does 
sometimes happen. 

869. Methods of Repairing. The repairs necessitated in 
the maintenance of an asphalt pavement may be classified as follows : 
(1) those due to a settlement of the subgrade; (2) those due to a 
disintegration of the pavement in spots; (3) those due to the forma- 
tion of waves; (4) those due to the formation of cracks; (5) the 
painting of the gutter; and (6) the remedying of defects next to the 
street-car rails, crossing stones, man-hole covers, etc. 

870. Settlement of Subgrade. Themajority of repairs are neces- 
sitated by the settlement of the foundation over trenches. To repair 
these defects, it is necessary to remove the wearing coat, the binder, 
and the foundation; and then, after having consolidated the material 
in the trench (see § 764), to re-lay the pavement much as in the original 
construction. The edges of the binder course and also of the wearing 
coat should be thoroughly covered with a thin coat of asphaltic 
cement to secure a perfect union of the old and the new material. 
Both the binder course and the wearing coat should be thoroughly 
tamped or rolled. Owing to the difficulty of fully consolidating the 
patch, it is left a trifle high to prevent a possible depression. 

871. Disintegration. If the wearing coat disintegrates in spots, 
or forms '' macaroons," from any of the causes described in § 848-65, 
the affected part must generally be cut out, since it is usually affected 
to its full depth. If the binder course is the cause of the deteriora- 
tion (see § 812), it also must be cut out. The new material is to be 
laid as described in the preceding paragraph. If the disintegration 
does not extend to the full depth of the wearing coat, the repair may 
be made by " skimming," as described in the succeeding paragraph. 

872. Formation of Waves or Humps. If the wearing coat has 
shifted under the traffic so as to form waves, i. e., until it is thicker 
in some parts than others, or if the wearing coat has crowded towards 
the gutter, it may be necessary to melt off a portion of the high part, 
and also to re-surface the thin part. This is called skimming. The 
asphalt is melted off either with an open grate on low wheels in which 
coke is burned; or with a special heater having a tank for gasohne, 
a hood over the burner, and an asbestos mat to protect the adjacent 
pavement. Fig. 161 shows one of several forms of surface heaters 
in common use. The surface is heated until the affected portion 
can be raked off; and then new material is added to bring the pave- 
ment to its proper thickness. 

" Whenever the surface-heater or skimming method is employed, 



450 ASPHALT PAVEMENTS [CHAP. XVl 

all defective surface shall be removed before replacing it with new 
material. In all cases the old sm^face shall be removed to a depth 
of not less than one quarter inch; and the new surface must, when 
compressed, be not less than one half inch in thickness. The heat 
shall be applied in such a manner as not to injure the remaining 




Fig. 161. — Sckface Heater for Repairing Asphalt Pavements. 

pavement. All burnt and loose material shall at once be com- 
pletely removed; and, while the remaining portion of tr^e old pave- 
ment is still warm, the new material shall be placed. The new 
and freshly prepared wearing coat shall be laid in strict accordance 
with the specifications for the original pavement." * 

873. Cracks. When cracks have formed in the wearing coat, 
all the loose material is cut off, the crack is cleaned out, and hot 
asphaltic cement is poured in. 

874. Painting Gutters. Owing to the disintegrating effect of 
water, asphalt gutters usually require comparatively frequent 
repairs either by painting with asphalt rich in bitumen, or by skim- 
ming (§ 872), or by removing the wearing coat and re-laying it, 
using an asphalt richer in bitumen than that in the remainder of 
the pavement. 

875. Recording Repairs. The present practice is to make the 
repairs to asphalt pavements by contract with a guarantee of the 
work for a number of years; therefore it is important that a record 
should be kept of the area and location of the several patches and 
also of the date when each was made. This is done by dividing 
the pavement into imaginary squares, say, 10 feet on a side; and 

* Specifications of Amer. Soc. ^of Municipal Improvements for Sheet Asphalt Pa^'ing, 
approved Oct. 14, 1915, p. 12. 



ART. 1] SHEET ASPHALT PAVEMENTS 451 

then when a patch is to be made, one or more of these squares should 
be located by chalk marks on the pavement, and the boundary 
of the patch should be sketched in a cross-ruled note-book. The 
records of the individual patches are afterwards platted upon a 
single sheet to see that a subsequent patch does not overlap one for 
which the guarantee has not expired. 

876. Using Old Materials. In some cities it is customary to 
permit the re-use of the old asphalt; but this is of doubtful widsom, 
since usually the repair is required by the inferiority of the old 
material, and since it is likely to be over-heated in being removed. 
If the asphalt is not damaged, and is cut out with an axe, it may be 
used again, provided (1) the pieces are kept clean, (2) it is re-heated 
slowly and carefully, and (3) new asphalt is added to flux the old. 
It is difficult to melt old material without burning it, and it is also 
difficult to secure a uniform mixture with it. 

877. COST OF Construction of Sheet Asphalt Pavements. 
Asphalt pavements are comparatively expensive, since the tools 
and machinery employed in mixing and laying the asphalt are 
costly and subject to large depreciation whether idle or in use, 
and also since the business requires a considerable proportion of 
skilled labor. One of the peculiarities of the business is the dis- 
proportionate amount of capital invested in the plant compared 
with the business done, often an expensive plant being maintained 
in a city for one or more years without laying any pavement or at 
most only a small amount. Or a portable plant is moved to a small 
city for a comparatively small amount of pavement. Another 
peculiarity is that the working season is short, extending only from, 
say, the first of May to the first of November; and as expert superin- 
tendents and foremen are indispensable, it is necessary to employ 
this skilled labor by the year. 

878. In connection with data on the cost of construction of a 
pavement, it should not be overlooked that the cost of the pavement 
proper is not usually the total cost which the property holder must 
pay for the improvement of the street when it is paved. Usually 
the improvement of the street includes four items, viz.: (1) excava- 
tion for the pavement, (2) the construction of curbs and gutters, 
(3) laying drains and building catch basins, man-holes, etc., and (4) 
the pavement itself. 1. Under ordinary conditions the excavation, 
exclusive of surfacing and rolling the subgrade, will cost 10 to 15 
cents per square yard. 2. Combined concrete curbs and gutters 
(§ 737), will usually cost 30 to 35 cents per square yard of pavement 



452 ASPHALT PAVEMENTS [CHAP. XVI 

3. The drainage will usually cost 10 to 15 cents per square yard 
of pavement. These three items may add 50 to 60 cents per square 
yard to the cost of the pavement proper. 

879. Estimated Cost. The estimate of the cost of laying an 
asphalt pavement shown in Table 45 was prepared for this volume 
by a man of acknowledged ability and unquestioned integrity, who 
has had 20 to 25 years' experience as an inspecting and consulting 
engineer of asphalt paving in various cities.* The estimate is for a 
city in which 100,000 square yards are laid in one year. 

The table is chiefly interesting as showing the items that go to 
make up the expenses which are separate and distinct from that for 
materials and labor. Of course, these expenses would be less or 
more per square yard, if the area of pavements laid was greater or 
less than the amount stated. The estimate is for first-class work 
under average conditions prevailing in 1916. 

880. Actual Cost. Table 46, page 454, shows the contract price 
for constructing sheet asphalt pavements in thirty-three cities. 

881. COST OF Maintenance. The cost of maintenance will 
vary with the original quality of the pavement, its age, the amount 
and nature of the trafiic, the width of the street, the presence or 
absence of street-car tracks, the frequency with which the pavement 
is cleaned and sprinkled, the climate, etc. 

In nearly all American cities there is a serious lack of data con- 
cerning the cost of maintaining pavements; and this lack is more 
serious for sheet asphalt pavements than other forms, since this type 
involves more variables. A few cities attempt to keep a record of 
the cost of maintaining pavements; but such records are often so 
incomplete and so incorrectly compiled as to be valueless. Some of 
the reasons for the dearth and incompleteness of the data on the 
cost of maintaining sheet asphalt pavements are as follows : 

1. The pavement is usually built under a long-time guarantee, 
and the city pays comparatively little attention to the quality of 
the materials used and the methods of construction employed; 
consequently there is no satisfactory record of the quality of the 
pavement. In some cases the date when the pavement was laid or 
re-surfaced is unknown ; and in many cities no adequate records are 
kept of the location of repairs or patches. In recent years cities 
are improving in this respect; but the usual absence of such records 

*A. W. Dow, for a numbet of years Inspector of Asphalt and Asphalt Paving for the Dis- 
trict of Columbia, and for several years past a consulting asphalt chemist and asphalt paving 
engineer in New York City. 



ART. 1] SHEET ASPHALT PAVEMENTS 453 

TABLE 45 

Estimated Cost op Sheet Asphalt Pavement 
Plant and Capital Charges: 

Interest on cost of fixed plant, — 5% on $13,500 $675.00 

Interest on cost of rollers, tools, etc., — 5% of $3,000 150.00 

Taxes,— 1% of $10,000 100. 00 

Insurance, — 4% of $10,000 400.00 

Depreciation,— 8% of $16,500 1,320.00 

Rental or interest on real estate, — 5% of $4,000 200.00 

Interest for 6 months on working capital, — 5% of $6,000. . . 150.00 

Current repairs 500 . 00 

Watchman for 1 year 400 . 00 

Total for 100,000 square yards $3,895.00 

Total for 1 square yard . 039 

Local Management and Clerical Expenses: 

Rent of office 1 year $400.00 

Telephone, light, water, etc 100 . 00 

Salary of superintendent, — 1 year 2,000 . 00 

Cashier in charge of office, — 1 year 1,200 . 00 

Clerks, timekeepers, etc., — 6 months 700 . 00 

Proportionate part of winter pay roll 750 . 00 

Total for 100,000 square yards $5,150. 00 

Total for 1 square yard .051 

General Officers and Offices: 

Laboratory and general expenses . 030 

Expense Securing Contracts: 

Agent's commission, legal and traveling expenses, etc . 050 

Material and Labor per Square Yard: 

Subgrade, — 0.25 cubic yard, grading, rolling, etc . 125 

Foundation,— 6 inches of concrete (1 P. C: 3 S.; 6 B. S.).. .700 

Binder — 1 inch complete . 170 

Wearing surface — 2 inches : 

22 lb. of asphalt cement at $20 per ton .220 

0.083 cubic yard sand at $1.20 100 

16 lb. pulverized limestone at $3.50 per ton . 030 

Fuel used at plant .020 

Oil, waste and simdries . 002 

Labor at plant . 060 

Hauling material to street . 030 

Laying and rolling . 050 

Total for materials and labor $1 . 507 

Cost of Guaranty: 

5 years at 2| cents per year 1 . 00 

Total cost of pavement, per square yard $1 . 777 



454 



ASPHALT PAVEMENTS 



[chap. XVI 



TABLE 46 
Cost of Construction of Sheet Asphalt Pavements 
Laid in 1916 



Ref. 
No. 



Locality. 



State. 



California. . . . 

Connecticut. . 

Dist. of Col . '. '. 
Illinois 

Indiana 

Iowa 

Kansas 

Kentucky. . . . 
Maryland. . . . 
Michigan. . . . . 
Minnesota. . . . 
Nebraska. . . . . 
New Jersey. . . 
New York. . . . 
North Carolin 
Ohio 

Pennsylvania . 

Texas 

Utah 

Washington. . . 
West Virginia. 
Wisconsin. . . . 



City. 



Long Beach 
San Diego. . 
Santa Monica 
Hartford. . . 
New Haven 
Washington 
Chicago 
Moline. 
Ft. Wayne 
Goshen. 
South Bend 
Vincennes 
Mason City 
Sioux City 
Newton. . 
Louisville. 
Baltimore 
Detroit. . . 
Duluth. . . 
Omaha. . . 
Elizabeth. 
Syracuse . 
Durham. . 
Cincinnati 
Lakewood 
Toledo. .. 
Xenia. . . . 
Pittsburg. 
Beaumont 
Ogden . . . 
Seattle. . . 
Charleston. 
Racine. . . . 



Amount 

Laid 
Sq. Yd. 



11972 
12 043 
34 910 
32 195 
92 742 
154 076 
1 248 000 
36 059 
45 112 

24 046 
18 702 

107 506 
131 489 

11000 
113 200 

47 747 
9 257 

12 40S 
21 300 
23 130 

25 000 

7 407 

8 000 
2 351 

13 790 
43 357 
25 000 
74 134 
66 727 
10 585 

146 173 

6 450 

20 851 



Concrete 
Base. 



3 : 6 
3 : 5 
3 : 6 

2 : 3 

3 :6 
3 :7 
3 : 6 
3 :6 
3 :6 
3 :5 
7G 

5 

3 :6 
2§ :4 

2 :4 

3 : 6 
a:6 
3 : 6 
3 : 6 
3 : 6 
3 : 6 
3 : 6 
3 :6 
3 : 6 
3 : 6 
3^ : 6 
3 : 6 
3 : 6 
2§ :5 
3 :6 
3 :6 
2i : 6 
3 : 5 



Binder 

Course. 



1" 
1" 
1" 

u 

1 
1 

H 
1 
1 
II 



n 

1 
li 

1 
n 

1 
n 

1 

"i'i' 

1 
1 
1 



eg 



5-8 



4-6 
5.5 



5-8 



5-8 



Wearing 
Coat. 



2" 
2" 

H 
H 

2i 

2 

2 

n 
n 

2 

n 
n 

2 
2 
2 

n 

2 
2 

U-2 

2 

H 

n 
u 

2 

u 

2 
U 

2 



Ah 



10-12 



11 

10.5 

11 



11 



10-13 



9-13 



.So 



m^6' 
^^ >-> 

m C! "K 

O e3 ft 

o 



$1.56 
1.50 
1.22 
1.58 
1.84 
1.66 
1.89 
1.81 
1.70 
1.56 



81 



10 
26 
74 
1.37 
2.04 
2.14 
1.90 
1.60 
1.68 
1.73 
2.25 
1.99 
1.99 
1.98 
2.15 
1.90 
1.80 
1.40 
1.86 
1.99 



in the past makes it impossible to make comparisons extending over 
any considerable length of time. 

2. There are almost no data as to the amount, nature and dis- 
tribution of the travel on city pavements (§ 34); and without such 
data it is impossible to determine the service obtained from a pave- 
ment or to make any accurate comparisons as to the cost of its 
maintenance. 

3. Many of the records that have been kept fail to discriminate 
between pavements on streets with and without street-car tracks; 
and even if they do state the presence of a street-car track, they 
often fail to state the method of computing the area maintained. 

4. Some cities include in the cost of maintenance the expense of 



*Municipal Engineering, Yol 52 (1917), p. 63-65. 



ART. 1] SHEET ASPHALT PAVEMENTS 455 

repairing cuts made by plumbers, gas-fitters, electricians, etc., which 
has nothing to do with the cost of maintenance proper, i. e., with the 
durability or wear of the pavement. 

5. In some cities the repairs are made by contract, and in some 
by the city's force. In some of the former cases, the amount of 
repairs is so small and other conditions are such as to eliminate com- 
petitive bidding; and hence the cost is abnormally high and con- 
sequently valueless. Sometimes when the repairs are made by the 
city's force, the record does not include all the elements of the cost. 
For example, the following items of cost are often omitted: (a) 
Interest on the cost of the plant and eq'uipment employed in making 
the repairs; (6) interest on working capital; (c) a charge for depre- 
ciation of plant and equipment; (d) a charge for supervision and 
office expense; and (e) material and labor supplied by other municipal 
departments. 

6. Almost no records of the cost of maintenance state anything 
as to the condition of the pavement at the beginning or the end of 
the period considered. It is probably impossible accurately to 
make such an inventory; but the bearing of such an inventory upon 
the results should at least be considered. The failure to consider 
this phase of the subject is the same as though a merchant should 
attempt to compute his annual profits without an inventory at the 
beginning and the end of his fiscal year. See §1232. 

882. Obviously it is practically impossible in any city to segre- 
gate the cost of maintenance according to the quality and the age 
of the pavement, the amount of travel, and the presence or absence 
of car tracks; but a considerable improvement upon the present 
practice of most cities is entirely feasible and very desirable. 

Owing to the dearth of accurate and definite data, it will not be 
possible to give much reliable or valuable information on the cost of 
maintenance of sheet asphalt pavements. Further, since few 
contractors are equipped especially for making repairs, and since the 
public has no knowledge of the cost of the work to the contractor, 
the only data submitted will be those obtained with municipal repair 
plants. 

In this connection it is not wise to consider pavements laid before 
about 1895, since before that time the importance of a proper 
gradation of the mineral aggregate was not understood, and con- 
sequently such pavements are likely to be much inferior to the best 
pavements laid later. 

883. Municipal Repair Plant. A sheet asphalt pavement when 



456 ASPHALT PAVEMENTS [CHAP. XVI 

constructed in accordance with good practice is a reasonably satis- 
factory and economical form of pavement; but it usually requires 
repairs at an earlier period in its life than most other pavements, 
and the total cost of maintenance during its useful life is also some- 
what greater. It is a high-grade pavement, and therefore should 
have more careful and skilful attention than most other paverfients. 
For these reasons the repair of a sheet-asphalt pavement when 
needed is a vitally important matter. In the early history of asphalt 
pavements the repairs were made by the contractor whose chief 
business was to build new pavements; but in recent years many 
cities have established municipal asphalt repair plants. The main 
conditions leading to this change in practice were as follows : 

1. Usually there was little or no competition among contractors 
for the contract to repair asphalt pavements. The equipment and 
skill required in laying sheet asphalt pavements is so great as usually 
to hmit the number of contractors doing this kind of work; and 
while competition with other forms of pavements is likely to keep 
the first cost of asphalt pavements within reasonable limits, there 
are so few asphalt-paving contractors that usually there is no com- 
petition for the maintenance of such pavements. With a municipally 
owned repair plant the city virtually becomes a competitor of the 
ordinary contractor. 

2. The plant and the other equipment for pavement construction 
is not suitable for pavement repairs. The construction plant and 
equipment is designed for turning out large quantities of material, 
while a repair plant should be designed for turning out small quan- 
tities. 

3. With a municipal repair plant old material may be used in 
repairing pavements that have about reached the end of their eco- 
nomical Ufe, and thus utiHze the old material without injuring the 
pavement. 

4. Since the repair plant is small, repairs may be made con- 
tinually and when needed, instead of being allowed to accumulate 
as usual under the contract method until enough repairs are called 
for to warrant either starting up a large plant or diverting the plant 
from new construction to repair work. 

884. The saving through the municipal repair plant has usually 
been quite considerable. Table 47 shows the results for Washing- 
ton, D. C, and is fairly representative of the results obtained in 
other cities. For a more detailed comparison for the experience 
of Brooklyn, N. Y., showing a more marked saving, see Engineering 



ART. 1] 



SHEET ASPHALT PAVEMENTS 



457 



and Contracting, Vol. 38 (1912), page 68; and for somewhat similar 
data for Niagara Falls, N. Y., see Engineering Record, Vol. 69 (1914), 
page 256. 

TABLE 47 

Cost op Repairs of Sheet Asphalt Pavements in Washington, D. C* 

Including coal-tar surface, and excluding all pavements under guaranty. 



Repaired by Contract. 


Repaired By Municipal 
Plant. 


Year. 


Cents per 
Sq. Yd. 


Year. 


Cents per 
Sq. Yd. 


1908 

1909 
1910 
1911 
1912 


3.8 
2.3 

2.6 
2.2 

2.4J 


1913 
1914 
1915 
1916 


2.0 
1.9 
1.9 
1.8 



885. Cost of Repairs. In Brooklyn with Municipal Plant. Table 
48 shows the detailed cost of making repairs to sheet asphalt 
pavements in Brooklyn, N. Y., with a municipal repair plant. 



TABLE 48 

Cost of Maintenance of Sheet Asphalt Pavements 
In Brooklyn^ N. Y., in 1911, with Municipal Repair Plant f 



Items of Expense. 



Supervision and fiLxed charges, 

Supplies, repairs, etc 

Materials 

Plant labor . 

Street labor 

Trucking 

Total 



Cost in Place per Cubic Foot of 
Uncompressed Mixture. 



Repairs. 



Wearing 
Coat. 



$0,025 
0.067 
0.178 
0.046 
0.182 
0.060 



$0,558 



Binder 
Course. 



$0,024 
0.057 
0.097 
0.043 
0.174 
0.057 



$0,452 



Repaying. 



Wearing 
Coat. 



$0,025 
0.059 
0.178 
0.046 
0.213 
0.080 



$0,601 



Binder 
Course. 



$0,024 
0.057 
0.097 
0.043 
0.203 
0.076 



$0,500 



In Buffalo by Contract. Buffalo, N. Y., has long been noted 
for the extent of its sheet asphalt pavements, and also for the 
accuracy and completeness of its records concerning the cost of 



* Private letter from Capt. J. J. Loving, Corps of Engineers, U. S. A., Assistant to the Engi- 
neer Commissioner of the District of Columbia. 

t Engineering and Contracting, Vol, 38 (1912), p. 68, 



458 



ASPHALT PAVEMENTS 



[chap. XVI 



repairs of pavements. The annual reports of the Bureau of Engi- 
neering contain voluminous statistics on the cost of construction 
and repair of all kinds of pavements. For example, the report for 
the fiscal year ending June 30, 1916, contains 179 pages of tabular 
matter showing the width, length, area, original cost, and the cost 
of repairs for each year after the expiration of the guaranty, of 
all the sheet asphalt pavements in the city. The report also 
gives a summary of similar data for several years back; and in 
addition contains several pages of data concerning the amount and 
age of all pavements, by whom built, the kind of materials 
used, etc. 

The annual cost of repairs in Buffalo from 1902 to 1916 for 
substantially 3,000,000 sq. yd., varied from 1.30 to 8.27 cents per 
sq. yd., the average for the fourteen years being 5.06 cents per 
sq. yd. 

The cost of maintaining 2,369,191 sq. yd. was 4.45 cents per sq. yd. 
per year; and the cost of repairs was 6.46 cents per sq. yd. per year. 
The average life of sheet asphalt pavements replaced between 1878 
and 1906, was 20.51 years, being 21.77 years for streets without car 
track and 18.36 for streets having car tracks. 

Table 49 gives some of the details concerning the cost of repairs 
of sheet asphalt pavement for the year ending June 30, 1916. 



TABLE 49 

Data on Repairs of Sheet Asphalt Pavements 

Buffalo, N. Y., 1915-16, by contract * 



Ref 

No. 


Items. 


Contract 
Price. 


Average 

Quantity 

PER Sq. Yd. 


Cost 

PER 

Sq. Yd. 


i 


July 1 to December 31, 1915: 

Wearing coat, per cubic foot 


$0.37 
0.17 

0.18 
0.51 


1.3673 
0.7276 
0.1205 


$0 5059 


2 
3 


Binder course (open), per cubic foot. . . . 
Asphalt cement, per gallon 


0.1237 
0217 


4 


Labor, per square yard 


51 




Total . 






5 


SI 1613 


6 


January 1 to June 30, 1916: 

T\^earing coat per cubic foot 


0.33 
0.17 
0.18 
0.47 


1.3843 
0.8570 
0.1204 


4568 


7 
8 


Binder course (open), per cubic foot .... 
Asohalt cement oer crallon . . 


0.1456 
0217 


9 


Labor oer souare vard . . • • 


0.47 










10 


Total 


$1.0941 











♦Annual Report Bureau of Engineering, 1915-16, p. 



ART. 1] 














SHEET 


ASPHALT 


PAVEMENTS 


















459 


Fig 
ments 

11 
10 


\. 162 shows the cost of repairs of sheet asphalt pave- 
at different ages. The pavements laid before 1898 were 


















































( 


> / 


/ 


^ 
























































/ 


/ 
























































; 


/ 






< 


> 












































c 


( 


) 


/ 

> 


c 


) 


















































( 


>/ 


/ 




) ( 

c 


> 
) 


( 


> < 


) 










































< 
( 




) 


f ( 


) 












\ 


» 


































( 


^ f 


/< 


/ 
























































( 
( 

/ 


> < 

k 


K 


) ( 


) 
















































( 


< 
V 


y* 


f 








/ 


1 


f 




























K 












y 


/ 


/ 


y 


















































.*'' 


1 


,^ 


y 


< 


> 



















































Fig. 



5 10 15 ZO 25 

Age of Pai^en7en/'- Years 

162. — Cost of Repairs or Sheet Asphalt Pavements in Buffalo. 



on a 5-year guaranty, and those after on a 10-year guaranty. The 

curve in Fig. 162 is that for — — , in which A is the age of the pave- 

ment in years. 

887. Maximum Grades for Asphalt Pavements. Until 
within a few years, it has been assumed that the maximum per- 
missible grade for a sheet asphalt pavement was 2 or 2\ per cent; 
but experience has shown that this limit is too low. It is now gen- 
erally conceded that sheet asphalt may be laid on grades of 5 or 
6 per cent, particularly in residence streets — where a clean, smooth, 
noiseless pavement is specially desirable, and where there is usually 
no great amount of travel. With a 5 or 6 per cent grade, there 
may be a few days each year when the pavement is icy and too 
slippery for either comfortable or safe use. In New York City, on 
a street having a 6 per cent grade paved with asphalt on the sides 



460 ASPHALT PAVEMENTS ' [cHAP. XVI 

and granite in the center, the traffic as a rule seeks the asphalt 
rather than take the granite; and in the same city traffic has de- 
serted one street having a 5 per cent grade paved with granite for 
another having a 6 per cent grade paved with asphalt. A number 
of cities have sheet asphalt pavements upon a 7 per cent grade, as, 
for example, Peoria, 111., Grand Rapids, Mich., Syracuse, N. Y., 
Troy, N. Y.; and Omaha, Neb., and St. Joseph, Mo., have asphalt 
pavements on an 8 per cent grade. Scranton, Pa., has a short piece 
of asphalt on a 13 per cent grade; San Francisco, Cal., a piece on a 
16 per cent grade; and Pittsburg, Pa., one on a 17 per cent grade. 
A committee of the American Society of Civil Engineers recom- 
mends 5 per cent as the permissible maximum grade for sheet asphalt 
— see Table 15, page 57. 

888. Crown for Sheet Asphalt Pavements. The special 

committee of the American Society of Civil Engineers recommends 
that the crown shall be between \ and \ of an inch per foot of the 
half width, see Table 16, page 65. 

889. Merits and Defects of Sheet Asphalt Pavements. 
The advantages possessed by monolithic asphalt pavements con- 
structed as described above are: (1) they produce neither dust nor 
mud; (2) they are comparatively noiseless, except for the clicking 
of the horses' shoes ; (3) they do not absorb or retain noxious Uquids, 
but facihtate their prompt discharge into the gutters and storm- 
water sewers; (4) they reduce the force of traction to a moderate 
amount (see Table 8, page 21); and (5) they afford a reasonably 
good foothold for horses. 

The defects of sheet asphalt pavements are: 1, the first cost is 
comparatively great; 2, the cost of maintenance is large; and 3, 
such pavements are generally considered too smooth for steep grades. 

For a discussion of the relative merits of the different pavements, 
see Chapter XX. 

890. Specifications for Sheet Asphalt Pavements. The 
American Society for Municipal Improvements on October 14, 
1915, adopted Specifications for Sheet Asphalt Paving, printed 
copies of which may be had of the Secretary of the Society for a 
nominal sum. The specifications cover only the selection, prepara- 
tion, and laying of the materials for the binder course and the 
wearing coat. These specifications are of the so-called blanket type, 
that is, they contain general requirements for the asphalt and 
asphalt cement which are intended to include all the different 
kinds of asphalt. 



ART. 2] ASPHALT-CONCRETE PAVEMENTS 461 

For a statement of the objections to this form of specification, 
see § 532; and for alternate restricted specifications for asphalt for 
other kinds of pavements, see § 534-41. 

Art. 2. Asphalt-concrete Pavements 

891. An asphalt-concrete pavement consists of a foundation of 
either bituminous or hydraulic-cement concrete, and a wearing coat 
of asphalt concrete. There are two differences between asphalt 
concrete and the bituminous concrete discussed in Chapter X, — 
Bituminous Macadam and Bituminous Concrete Roads. 1. Asphalt 
concrete is made with asphaltic cement, while the bituminous con- 
crete may be made with either asphalt or tar. 2. Bituminous con- 
crete is made with only the care usually employed in making 
hydraulic cement concrete, while asphaltic concrete is usually pro- 
portioned, mixed and laid with approximately as much care as sheet 
asphalt pavements. 

The difference between a sheet asphalt pavement and an asphalt- 
concrete pavement is in the maximum size of the aggregate. In 
the former all of the aggregate will pass a No. 8 sieve, while the latter 
may contain l§-inch stone. The ordinary sheet asphalt pavement 
could with some propriety be called a sand asphalt pavement or an 
asphalt mortar pavement, to distinguish it from an asphalt con- 
crete pavement. 

892. Definitions. There are several types of asphalt-con- 
crete pavements, the best known of which are : Bituhthic, Warrenite, 
Amiesite, and asphalt concrete. 

893. Bitulithic Pavement. This is a patented form of pave- 
ment in which the wearing coat is composed of bitumen and mineral 
aggregates ranging from 3 inches down to an impalpable powder. 
The bituminous mixture is usually mixed in a non-portable plant. 
The aggregate is chiefly crushed stone; and the aggregate of the 
seal coat is stone chips. 

Six patents (No. 727,505 to 727,512) were issued to Frederick F. 
Warren, Newton, Mass., between May 16, 1901, and April 14, 1902, 
for preparing asphalt for paving purposes and for closely related 
forms of asphalt-pavement construction. Of the eighty-two speci- 
fications in these patents, sixty-five relate to the proportions and 
method of laying the pavement. Apparently the intention is to 
cover such gradations of the ingredients as will secure maxinmm 
density and maximum stabihty. The density of a sheet asphalt 



462 ASPHALT PAVEMENTS [CHAP. XVI 

pavement made with limestone filler is 2.20 to 2.22 (§ 832); but the 
density of a bitulithic pavement made of the same materials may be 
2.28, and if the bitulithic is made of trap the density may be 2.50 
or even more. This type of pavement is designed for city streets 
and it has been largely used for this purpose (see page 320). 

894. There has been much controversy and considerable litigation 
as to the scope and meaning of these patents, and it is impossible 
to state in a single series all the gradations included. Two gradings 
actually employed in laying bitulithic pavements are shown in 
the following table. 

Gradings of Wearing Coat of Bitulithic Pavements * 

No. 1. No. 2. 

Bitumen 7.6% 7.02% 

Mineral aggregate passing 200-mesh 4.9 4 . 58 

100-mesh 4.6 3.99 

80-mesh 3.2 2.76 

50-mesh 7.3 7.88 

40-mesh 3.1 1.27 

30-mesh.... 2.4 2.39 

20-mesh 2.2 2.13 

10-mesh 5.1 3.77 

i-inch 9.1 4.85 

Hnch 19.3 12.75 

li-inch 31.2 46.61 



Total 100.0% 100.00% 

* Agg's Construction of Roads and Pavements, p. 308. 

895. Warrenite Pavement. This type of pavement is covered 
by the Warren patents (§ 893); and is especially designed for rural 
roads. The mixing is usually done in a semi-portable plant; and 
the ingredients are not proportioned with as much care as for bitu- 
lithic pavements (§ 893). Sand is largely used in the body of the 
wearing course and wholly for the seal coat. 

896. Amiesite Pavement. This is a proprietory mixture of 
asphalt cement, sand, and broken stone up to Ij inches in diameter. 
It is mixed at a plant, and is shipped in cars to the city where it is 
to be laid. During transit the mixture cements into a soHd mass, 
and must be heated before it can be shoveled from the car. To 
heat it, holes are dug into the mass and steam is blown into them 
and permeates the whole mass and softens it. This type of pavement 
is laid without a concrete base. The mixture is laid cold, usually in 
two courses, the lower being 2J or 3 inches thick, and the wearing 
coat 1 or 1| inch. 



AKT. 2] 



ASPHALT-CONCRETE PAVEMENTS 



463 



897. Topeka Mixture. An asphalt pavement somewhat hke 
the patented bituhthic pavement was laid in Topeka and Emporia, 
Kansas; and as a result of a suit for infringement of patent No. 
727,505, the U. S. Circuit Court in 1910 decided that the following 
gradation did not infringe said patent: 

Bitumen 7 to 11 per cent 

Mineral aggregate passing 200-mesh 5 to 11 " " 

" " " 40-mesh 18 " 30 " " 

10-mesh.. . 25 " 55 " " 

4-mesh 8 " 22 " " 

2-mesh not over 10 " 

The sieves are to be used in the order named. 

Notice that the aggregate is mostly sand, and J-inch and i-inch 
stone. Notice also that a wide variation in the grading is possible 
under the above specifications; and consequently many somewhat 
different gradings have been designated as Topeka mixture. Since 
1911 many thousands of square yards of roads and pavements have 
been laid under the above so-called Topeka specifications. 

898. The American Society of Municipal Improvements recom- 
mends the following grading,* which the Warren Brothers Co. has 
agreed does not infringe its patents, f 

Bitumen 7 to 9 per cent 

Mineral matter passing 200-mesh 7 "10 " 

80-mesh 10 " 20 " 

40-mesh 10 " 25 " 

20-mesh 10 " 25 " 

8-mesh 10 " 20 " 

4-mesh 15 " 20 " 

2-mesh 5 " 10 " 

899. Asphalt paving blocks (see Art. 4 of this chapter) have long 
been made of a mixture substantially the same as the so-called 
Topeka mixture. 

900. Stone-filled Sheet-Asphalt Pavement. The so-called To- 
peka mixture is frequently described as the wearing-coat mixture 
for a sheet asphalt pavement to which has been added J-inch and 
J -inch broken stone; and is sometimes referred to as a stone-filled 
asphalt mixture, and also as a fine asphaltic concrete. 

Mr. Clifford Richardson, a recognized authority on asphalt 
paving, in Engineering Record, Vol. 65 (1912), page 718, and 
again in Vol. 70 (1914), page 634, shows that for the best 



* Proceedings, 1915, p. 415. 
f Ibid., V. i23. 



464 



ASPHALT PAVEMENTS 



[chap. XVI 



results possible within the Hmits of the above decree, the finer 
part of the mixture should conform to the standard grada- 
tion for sheet asphalt (§ 827) and that as much as J-inch and J-inch 
broken stone should be added as the ruling of the court will 
permit. He states that the two gradings in Table 50 have given 
satisfaction. The one on Riverside Drive was laid in 1913; and 
the one in Rochester has been in use since about 1902. Mixtures 
of this type have been laid extensively in the last few years. 



TABLE 50 

Composition of Stone-filled Sheet Asphalt Pavement 

(Best Topeka Mixture) 



Ingredients. 


Riverside Drive, 
N. Y. City. 


Rochester, N. Y. 


Total 
Mixture. 


Finer 
Portion. 


Total 
Mixture. 


Finer 
Portion. 


Bitumen 

Mineral matter passing 200-mesh 

" " " 80-mesh 

" " " 40-mesh 

" " " 10-mesh 

" " " 4-mesh 

" " " 2-mesh 


8.9% 
11.9 
14.5 
18.6 
18.9 
19.1 

8.1 


11.1% 

16.5 
20.1 
25.9 
26.4 


8.9% 
12.3 
10.8 
24.2 
16.2 
21.5 

5.4 


11.1% 

17.1 
15.0 
33.7 
22.7 


Total 


100.0% 


100.0% 


100.0% 


99.6% 





901. Asphalt-concrete Pavement. An asphalt-concrete pave- 
ment, in a narrower sense than the way in which that term is used in 
the heading of this article, is a pavement in which the gradation of 
the aggregates is not as carefully made as in the four forms just 
mentioned. It is essentially a bituminous concrete (Art. 2, Chapter 
X), in which the bituminous cement is asphalt. 

The standard specifications of the American Society of Municipal 
Improvements for asphalt concrete, provide a wearing surface of 
asphalt cement and broken stone, and require the following gradation 
of the broken stone: '^ All of the broken stone shall pass a li-inch 
screen; not more than 10 per cent, nor less than 1 per cent, shaU be 
retained upon a 1-inch screen; and not more than 10 per cent, nor 
less than 3 per cent, shall pass a J-inch screen." 

902. Mixing and Laying Asphalt Concrete. The method 
of mixing and lajdng is substantially the same whatever the gra- 
dation of the aggregate. With the most careful grading the aggre- 
gate is usually heated and then separated into three sizes, not includ- 



ART. 2] ASPHALT-CONCRETE PAVEMENTS 465 

ing the dust or filler. Each size is stored in a separate bin. The 
predetermined weight of each size is drawn from the bin into a box 
resting upon a scale platform. The proper amount of asphalt cement 
is determined by weight. The mineral matter and the cement are 
heated separately to the proper temperatures, and are then put into 
a mixer somewhat like that shown in Fig. 146, page 419. The lim- 
iting temperatures are substantially the same as for the wearing 
coat of sheet asphalt pavements (§ 838). 

An asphalt concrete pavement is usually laid without any binder 
course, as the wearing course has sufficient stability to prevent its 
flow or displacement under travel. 

The mixture is hauled to the street, dumped, spread and raked, 
much the same as for the wearing coat of a sheet asphalt pavement 
(§ 839^0). 

The rolling of an asphalt concrete pavement is a very important 
matter. The weight of the roller and the temperature at which 
the concrete is roUed depends upon the type of the mixture. The 
roUer should be as heavy as possible without displacing the paving 
material. The large aggregate gives the mixture comparatively 
great stability, and hence it does not squeeze out under the roller 
as does the sand- or sheet-asphalt mixture; and therefore it is best 
to begin rolUng as soon as the mixture is spread. The rolling is 
usually done with a tandem roller weighing 8, 10, or 15 tons; or 
with a roller of the three-wheel type weighing 10 tons. The rolling 
should be continued until the roller no longer leaves a mark upon 
the surface. The early and heavy rolling aids in securing a firm 
union between the asphalt concrete and the base or foundation. 

903. After the rolling is completed, a coating of hot asphalt 
cement is appHed to the surface of the pavement at the rate of about 
i to ^ gallon per square yard, which is immediately covered with a 
layer of hot J- to f-inch stone chips at the rate of about 25 lb. per 
square yard. The pavement is then again rolled until the chips are 
firmly bedded in the cement, and until the surface is dense and 
waterproof. This seal coat is an essential feature of an asphalt- 
concrete pavement, since except the best bitulithic the body of the 
asphalt concrete is not waterproof. 

904. Cost of Asphalt-concrete Pavements. Topeka 
Mixture. Table 51, page 466, is an accurate analysis of the cost to the 
contractor of lajdng 18,000 square yards of Topeka asphalt-concrete 
pavement in Albany, Oregon, in 1916. The pavement consisted 
of a 3j-inch asphalt-concrete base, and a IJ-inch top of Topeka 



466 



ASPHALT PAVEMENTS 



[chap. XVI 



mixture. The base and top were spread and rolled separately. For 
similar data, giving almost the same results, for another contractor 
in the same city the preceding year, see Engineering News, Vol. 73 
(1915), page 1038. 

905. Various Cities. Table 52, page 467, shows the composition 
and cost of the several types of patented asphalt-concrete pavements 
in 33 cities. Table 52 was compiled from the statistics from 142 
cities, and contains all the places for which the data were complete. 

906. MERITS AND Defects of Asphalt-concrete Pave- 
ments. The merits and defects claimed for asphalt-concrete pave- 
ments are: 1. An asphalt concrete pavement, in the broader mean- 
ing of that term, is cheaper than the sheet asphalt pavement, since 
the use of the coarser material reduces the voids and also the surface 



TABLE 51 
Detailed Cost of Topeka Asphalt Pavement 
Average for one week's run 





Cost 


PEE Square 


Yard. 


Items. 


3§-inches 
Base. 


1 ^-inches 
Top. 


5-inches. 
Total. 


Materials: 

Gravel @ $0.86 per cubic yard 

Sand, fine @ $L50 per cubic yard 

coarse @ $1.80 per cubic yard. .... 

Asphalt @ $12 per ton 

Fuel oil @ $1.25 per bbl 

Wood @ $4 per cord 

Coal 


$0,062 
0.026 
. 024 
0.078 
0.016 
.005 
.005 


$0,013 

0.032 
0.058 
0.089 
0.008 
0.002 
0.003 


$0,075 

0.058 
0.082 
0.167 
0.024 
0.007 
0.008 


Total for materials 


.216 

0.052 
0.044 
0.013 


.205 

0.031 
0.032 
0.008 


.421 


Labor: 

Plant 


0.083 


■ Street. . . .' 


0.076 


Teams 


0.0021 






Total for labor 


0.109 


0.071 


0.180 


General Expense: 

Mixing plant, interest, depreciation, repairs 
Roller and small tools 


10 






0.05 








0.08 


Profits 






0.08 
















.31 










Grand total 






.96 











Engineering News, Vol. 76 (1916), p. 103. 



ART. 2] 



ASPHALT-CONCRETE PAVEMENTS 



467 



to be covered with cement, and hence less bitumen is required. The 
difference in bitumen is from 1 to 3 per cent. 2. An asphalt-con- 
crete pavement is cheaper than a sheet asphalt one, since the former 
is laid in a single course. 3. An asphalt-concrete pavement is less 
slippery than a sheet asphalt pavement, owing to the use of the stone 
fragments. 

But, on the other hand, an asphalt-concrete pavement will not 
endure under heavy travel, particularly horse-drawn steel-tired 
traffic, as well as a sheet asphalt pavement, since sooner or later 
the larger stones will be fractured and leave two uncemented sur- 
faces which will permit motion, wear and disintegration. 

TABLE 52 

Cost of Patented Asphalt-concrete Pavements * 

Laid in 1916 



Ref. 
No. 



Locality. 



State 



City. 



Area 

Laid, 

Sq. Yd. 



Concrete Base 



Thick- 
ness. 



Propor- 
tions. 



Thick- 
ness of 
Wear- 
ing 
Coat. 



Cost of 

base 
and top 
Sq. Yd. 



BiTULiTHic Pavement 



Arizona 

California 

Iowa. 

Minnesota. . . . . . 

New Jersey. . . . 

New York 

North Dakota. 

Ohio '. 

South iDakota. . 

Texas 

Wyoming 

California 

Connecticut. . . 

Montana 

New York 

North Carolina 

Connecticut. . . 
New York 



Douglas 

Tucson 

Los Angeles 

Richmond 

Santa Monica. . . 

Creston 

Knoxville 

Mt. Pleasant. . . 

Eveleth 

St. Cloud 

Virginia 

Billings 

Harrison 

Irvington 

New Brunswick . 
Binghamton ... 

Herkimer 

New Rochelle. . 

Bismarck 

Fargo 

Cincinnati 

Lakewood 

Sioux Falls 

San Antonio ... 
Sheridan 



28,000 

67 219 

104 672 

95 682 

15 870 

47 431 

13 660 

27 600 

20 004 

4 626 

1864 

35 893 

18 512 

7 472 
89 319 

8 147 
8 680 

17 132 
25 000 
35 712 

10 914 
4 112 

42 734 

11 880 
4 941 



Wakrenite Pavement 



Berkeley. . . 
Winsted. . . . 
Great Falls . 

Elmira 

Raleigh. . . . 



Amiesite Pavement 



Danbury 

New Rochelle. 
Salamanca . . . 



3 : 6 
3 :6 

3 : 6 
3 :5 



2i 
2 
2 
2 
2 
2 
2 
2 
2 
U 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 



23 900 


6 


1:3:6 


2 


9 801 


6 


stone 


2 


18 830 


4 


1:3:5 


2 


16 644 


5 


1 : 2i : 5 


2 


80 000 


4 


1:3:6 


2 



8 000 
19 297 
12 215 




macadam 


2 

2 
2§ 




stone 



$2.35 
2.16 
1.58 
2.16 
1.40 
1.89 
1.98 
1.89 
2.50 
2.15 
2.44 
1.91 
2.29 
2.40 
2.65 
2.30 
2.18 
1.50 
2.38 
2.14 
2.57 
2.20 
2.10 
2.30 
2.12 



1.40 
1.35 
1.90 
2.25 
1.52 



1.05 
1.29 
1.65 



* Municipal Engineering, Vol. 52 (1917), p. 248-49. 



468 



ASPHALT PAVEMENTS 



[chap. XVl 



Table 53 shows the composition and cost of the non-patented 
asphalt-concrete pavements in 32 cities. 

TABLE 53 

Cost op Non-patented Asphalt Pavements * 

Laid in 1916 



Ref. 
No. 



Locality. 



State. 



City. 





Concrete Base. 












H-l 








o 


O 


Amount 


m 




03 


^ ^ 


Laid, 


s 




(U O CO 




Sq. Yd. 


^ 


Propor- 


C1T3 b 


= ?« 






tions. 


;5mu 


Wi> 




H 




H 


H 



Cost of 
Base, 
Binder, 
and 
Wear- 
ing 
Coat. 



ToPEKA Mixture 



California. ... 

Iowa 

Kansas 

Michigan 

Missouri 

Nebraska 

North Carohna 
Texas 

Alabama 

Illinois 

Indiana 

Iowa 

Kansas 

Kentucky .... 

Michigan 

Minnesota 

Mississippi . . . . 

Nebraska 

New Jersey. . . . 
New York 

Ohio .'. . . 

Oregon 

South Carolina. 
South Dakota., 
Tennessee .... 

Texas 

Utah 

Washington. . . 
West Virginia. . 
Wisconsin .... 



I Berkeley. . . 
Fort Dodge. 
Great Bend. 
Topeka . . . . 
Ludington. . 
Springfield. . 
Norfolk . . . . 
Raleigh . . . . 
Taylor 



36 6G0 


5" 


1:3:6 




2" 


40 000 


5 


1:3:5 




2 


41 800 


4 


1 :2i :5 




2 


64 120 


5 


1 : 2| : 5 




2 


700 


6 


1 :6 




2 


7 073 


4 


1:3:7 




2 


63 000 


6 


1 :5G 




2 


70 000 


4 


1:3:6 




2 


130 000 


4 


1 :2 :4 




2 



Asphalt Concrete 



Gadsden 

LaGrange . . . . 

Oak Park 

South Bend. . . 
Cedar Rapids . 
Webster City . 

Emporia 

Manhattan. . . 

Louis ille 

Grand Rapids. 

St. Paul 

Greenwood. . . 

Beatrice 

Trenton 

Batavia 

Niagara Falls . 

Toledo 

Portland 

Greenville. . . . 

Mitchell 

Chattanooga. . 

Houston 

Salt Lake 

N. Yakima. . . 
Charleston. . . . 
Fond du Lac. . 





5" 




2 : 5 


2" 


2" 


23 171 


6 




3 : 6 




2 


185 241 


6 




3 :6 




2 


37 444 


5 




7G 






35 000 


4 




3 :5 




2 


16 622 


5 




3 : 6 




1* 


9 875 


4 




2f :5 




2 


39 930 


5 




5 




2 


20 092 


6 




3 :6 




2 


14 110 


5 




3- : 7 




2 


91690 


5 




25 :5 




2 


8 930 


4 




3 : 5 




2 


36 100 


5 




3 :6 




2 


23 334 


5 




3 :6 




2 


1800 


5 




21 :5 




seal 


4 560 


6 




3:6 




2 


12 174 


6 




3i :6 




2 


18 313 


5 




3 :6 




U 


62 000 


4 




3 :6 




2 


26 512 


5 




5§ 




2 


32 126 


5 




3 :6 




2 


126 917 


6 




3 : 6 




2 


12 200 


4 




3 :6 





2 


39 593 


4 




4 :6 




2 


96 690 


5 




2\ :5 




2 


22 475 


5 




3 :5 




2 



$1.18 
1.57 
1.26 
1.35 
1.05 
1.22 
1.51 
.63 
1.40 



1.36 
1.36 
1.55 
1.45 
1.49 
1.65 
1.27 
1.22 
1.68 
1.65 
1.60 
1.48 
1.57 
1.75 
1.75 
2.40 
1.85 
1.30 
1.30 
1.80 
1.46 
1.80 
1.75 
1.17 
1.78 
1.53 



* Municipal Engineering, Vol. 52 (1917), p. 193-95. 

907. Specifications. The American Society of Municipal 
Improvements on October 14, 1915, adopted complete '' Specifica- 
tions for Bituminous Paving," in which the binding material was the 
asphalt specified therein; but in 1916 the Society amended the gen- 
eral specifications by eliminating the special requirements for asphalt, 
and stating that the asphalt, the flux, and the asphalt cement should 
conform to the requirements for these materials given in the Spe- 
cifications for Asphalt Paving (§ 542) . Printed copies of the amended 



I 



ART. 3] ROCK ASPHALT PAVEMENTS 469 

specifications for " Bituminous Asphalt Concrete Paving " (Asphalt 
Concrete Pavements) may be had of the Secretary of that Society 
for a nominal sum. 

With the above Specifications are printed also specifications for 
the wearing coat of Bitulithic Pavements. 

908. The above Society also publish Specifications for Bituminous 
Concrete Pavements in which the mineral aggregate is the com- 
plete product of a stone crusher and in which the binding material 
may be any one of the asphalts described in § 539-40 or either of 
the two tars described in § 574-75. 

Art. 3. Rock Asphalt Pavements 

910. A rock asphalt pavement is made by crushing asphaltic 
limestone or sandstone, and laying it while hot upon a concrete 
foundation. In Europe this is the common form; and when the 
term asphalt pavement is used there, this kind is intended. 

Rock asphalt pavements have been laid only to a comparatively 
small extent in America. Rock asphalt pavements have been used 
in a small way in California for many years, and San Francisco, 
Los Angeles, and other cities have several miles of such pavements. 
Apparently both asphaltic limestones and sandstones are used in 
California; but the most of the so-called rock asphalts used for 
paving purposes are asphaltic limestones. 

A bituminous limestone to be suitable for paving purposes 
should be as coarse-grained as possible, should contain between 9 
and 10 per cent of bitumen soluble in carbon bisulphide, and should 
contain very little matter volatile below 400° F. Often one or more 
natural rocks are mixed to secure the proper proportion of bitumen; 
and sometimes a natural asphalt is added to the natural rock to 
increase the proportion of bitumen. 

911. Construction. The asphaltic rock is quarried, and 
then crushed to about egg size by toothed rollers. These pieces 
are first reduced to powder and then sifted to uniform fineness. 
The powder is dropped through a hopper into a revolving cylinder 
like a coffee roaster, which is about 6J feet in diameter, and is sur- 
rounded by a chamber the air in which is heated by a movable 
furnace placed just below it. The cylinder itself revolves and, 
since it is provided with blades arranged in screw form, the pow- 
dered rock is well mixed with hot air and is thus thoroughly heated 
to a temperature between 300° and 350° F. Specifications fre- 



470 ASPHALT PAVEMENTS [CHAP. XVI 

quentl}?- permit the rock asphalt to be heated to but 200° to 250° F. 
When the powder ^.s hot enough, the furnace is removed from under 
the heater and a cart replaces it, into which the asphalt powder is 
discharged and hauled to the street. The powder will retain its 
heat for several hours and so admits of being carted long distances 
without losing its heat, thus doing away with the necessity of having 
roasters at the point where the surface is to be laid, as was at one 
time the practice. For the best results, the mixture should be 
deHvered upon the street at a temperature of not less than 250° F., 
although specifications sometimes permit a temperature of but 
190° F. 

The heated powder is spread upon the concrete base to a uniform 
thickness about 40 per cent greater than that required for the fin- 
ished pavement. This must be done with great care in order that 
the material, which while hot has a great tendency to consolidate, 
may not be denser in one spot that another. The material is com- 
pacted by rolling in much the same way as is described for the arti- 
ficial asphaltic paving compound, except that as a rule the natural 
rock asphalt is not consolidated to so great an extent as is customary 
in laying the artificial mixture. The evidence of this is that a rock 
asphalt pavement will continue to shrink in thickness under traffic 
for a year or two; while the artificial mixture shrinks but little, if 
any, after completion. 

912. The general appearance of the completed pavement is 
much the same as that of the pavement made of the artificial mix- 
ture, except that the European rock pavements are lighter in color. 
The claim is that European natural rock asphalt pavements are 
more slippery and less susceptible to changes in temperature than 
are American artificial asphalt pavements. 

Not infrequently the term rock asphalt pavement is inappro- 
priately applied to a pavement made of an artificial mixture of sand 
and of asphalt extracted from a natural rock. 

Art. 4. Asphalt-block Pavements 

913. There are two general forms of asphalt pavements, the 
sheet or monolithic and the block. Three forms of the first have been 
fully described in the three preceding articles. The asphalt-block 
pavement is constructed by first molding rectangular blocks com- 
posed of asphaltic cement and crushed stone, and then placing these 
blocks side by side upon a gravel or concrete foundation. In 1909 



I 



ART. 4] 



ASPHALT-BLOCK ^AVEMENTS 



471 



there were in this country about 5,500,000 square yards of asphalt 
block pavement, see page 320. 

Fig. 163 shows a perspective view and cross section of a carriage 
way and foot way paved with asphalt blocks. 




Fig. 163. — Asphalt-block Pavement. 



914. The Blocks. At first crushed hmestone was used, but 
now the blocks are made with crushed trap, granite, or gneiss. 
The asphaltic cement is mixed substantially as for sheet pavements. 
The proportions employed in making the blocks vary slightly with 
the climate, and considerably with the fineness of the crushed stone; 
but are about as follows : 

Asphaltic cement 6 . 5 to 8 per cent 

Limestone dust 10 " 15 " " 

Crushed stone 67 " 78 " " 

Since the blocks contain larger fragments than sheet pavements, 
they contain a smaller per cent of voids, and hence can be made 
with a slightly smaller per cent of bitumen. 

The ingredients are mixed and heated about as for sheet pave- 
ments, and are then molded while hot under heavy pressure. For- 
merly the blocks were made 5 X 12 X 4 inches deep; and later they 
were 4 X 12 X 3 inches deep, and also 5 X 12 X 3 inches deep; 
but the blocks are usually 5 inches wide, 12 inches long, and 2, 2J 
or 3 inches deep according to the traffic conditions. Tiles are made 
now 8X8X2 inches deep ; and also with a hexagonal top surface 
having the same area as the square tile. The blocks are used for 
carriage ways, and the tiles for foot ways. 

The blocks are usually moulded under a pressure of about 2 



472 



ASPHALT PAVEMENTS 



[chap. XVI 



tons per square inch; and must be manufactured at such a temper- 
ature that the materials will press together in a mass having a spe- 
cific gravity of not less than 2.5 if made of trap, and of not less 
than 2.35 if made of limestone. 

915. The blocks are laid on a sand cushion or on a half-inch 
mortar bed on a portland concrete foundation — recently the latter 
is more common. After the blocks are laid, the surface of the pave- 
ment is covered with clean, fine sand or hard fine stone screenings, 
which are swept into the joints. The joints are not usually filled 
with a bituminous cement, as the blocks are malleable, and there- 
fore travel soon seals the joints and makes the pavement prac- 
tically water-tight. 

916. Cost. Table 54 shows the cost of asphalt block pave- 
ments in several representative cities. 

TABLE 54 

Cost of Asphalt Block Pavements * 

Laid in 1912 



Locality. 


Amount 

Laid 
in 1912 
Sq. Yd. 


Concrete Base. 


Depth of 

of 
Blocks. 


Averate 
Cost in- 


State. 


City. 


Thick- 
ness. 


Propor- 
tions. 


cluding 

Base and 

Grading 

per Sq. Yd. 


New York 


Jamestown 

Niagara Falls 

Port Chester 

Rye 


13 408 

56 619 

7 117 

9 800 

18 500 

4 800 
3 800 

5 083 

19 000 
51800 

6 000 

5 992 
13 000 

6 185 


5" 
5 

4 

f 

6 
5i 


1 : 2^ : 5 

1:3:6 

1:3:6 


¥ 

3 
2 

11 


$2,941 




3.201 


'• 


2.132 


• < 


2.56 


11 


Rye 

W. New York 

Ashland 




2 20 


New Jersey 


1:3:5 
1 : 2^ : 5 
1:3:5 
1:3:4 


2.65 


Ohio 


1 94 


Michigan 


Highland Park 

Mt. Clemens 

Savannah 

Way Cross 


2.251 




2.08 




1.73 










2 10 




4 
4 


1:3:6 
1:3:7 


2i 


2.95 




Toronto 


3 42 


• • 




2.65 















1 Includes curbs. 

2 Does not include curbs. 

* Engineering and Contracting, Vol. 39 (1913), p. 373. 



917. Merits and Defects. The advantages claimed for a 
pavement of asphalt blocks over a continuous asphalt sheet are: 

1. It is less slippery, owing partly to the joints and partly to the 
roughening of the surface due to the use of a hard crushed stone. 

2. It can be laid like any block pavement, and at the same time has 
almost the continuity of a sheet asphalt pavement. 3. It can be 
laid in cities where there is no asphalt plant. 4. It can be repaired 
by removal of individual units by common labor without expensive 



AKT. 4] ASPHALT-BLOCK PAVEMENTS 473 

plant and expert labor. 5. Having numerous joints, it is free from 
irregular and unsightly contraction cracks. 

The disadvantages of an asphalt block pavement in comparison 
with a continuous asphalt sheet are: 1. Its first cost is more, since 
the wearing coat of the block pavement is 2 inches or more thick, 
while that of the continuous sheet is at most only 2 inches. 2. 
The edges of the blocks chip off, and the pavement wears rough. 
3. It is sUghtly more noisy. 4. Owing to its numerous joints, 
it is less sanitary. 5. It is more expensive to clean. 6. Unless 
bedded with unusual care, the blocks have a tendency to crack. 
7. It is less durable, particularly under heavy or even moderate 
trafl&c. 8. The blocks are not rigid, and do not hold their shape 
as well as other paving blocks; and hence the pavement is not as 
easy to repair as other block pavements. 



CHAPTER XVII 
BRICK PAVEMENTS 

920. A brick pavement consists of brick set on edge on a suit- 
able foundation — either concrete, gravel, or native soil. Brick 
pavements have been used in Holland for perhaps a century, and to 
a much less extent and for a shorter period in northern England. 
Brick pavements were first used in the United States in 1870 at 
Charleston, W. Va., a place having a population of 12,000. An 
experiment was tried with a short section — less than a block; — 
and in 1873 a block on the principal business street was laid with a 
good quality of building brick, and remained in service until 1909 — 
36 years. A block of brick pavement, laid in 1875 on a leading 
business street of Bloomington, IlHnois, a place of 20,484 popula- 
tion in 1890, though constructed of an inferior building brick made 
of a superior clay, continued in service for 20 years. 

At present brick is the chief paving material employed in most of 
the smaller cities of the Mississippi Valley, and it is used exten- 
sively in many of the larger cities in that territory. In all parts of 
this country, the use of brick for residence streets and Ught traffic 
business streets is rapidly increasing. For the relative amount of 
brick pavements in use, see page 320. Notice that in yardage of 
what may be called durable pavements, brick ranks second. There 
are in this country nearly two hundred plants devoted to the man- 
ufacture of paving brick, some having annual outputs of 60,000,000 
to 100,000,000 bricks. 

921. The term brick pavements will be used in this chapter as 
including the brick v/earing coat of both rural roads and city streets. 
The discussion will primarily be made with reference to city pave- 
ments, since in extent they exceed rural roads; but later brick-paved 
rural roads will be considered. 

474 



ART. 1] THE BRICK 475 



Art. 1. The Brick 

922. A paving brick is simply a brick which, owing to careful 
selection of the clay and to skilful manufacture, is so hard and 
tough that it will resist the crushing and the abrading action of 
the travel. 

923. The Clay. Three distinct classes of clay may be em- 
ployed in the manufacture of paving brick: surface clays, impure 
fire clays, and shales. Surface clays are almost exclusively used for 
the manufacture of building bricks; and are not ordinarily suitable 
for ma'king paving bricks, since it is practically impossible to burn 
them hard enough without their losing their shape. On account 
of its infusibihty, pure fire clay is unsuitable for making paving 
brick, the brick being expensive to burn and lacking density, hard- 
ness, and strength; but quite impure fire clay makes a fair quality 
of paving brick, although the process of manufacture is compara- 
tively expensive. Bricks made from impure fire clay are usually 
Hght in color, varying from cream to buff, and ordinarily are quite 
porous, absorbing from 2.5 to 5.0 per cent of water. Most paving 
bricks are made from shale, — an impure, hard, laminated clay 
which has been subjected to great pressure by the superincumbent 
earth strata. Shale is widely distributed, and usually makes a 
better and cheaper paving brick than either surface or fire clay, 
although some fire clays make excellent paving bricks. 

The different classes of clay so shade by imperceptible degrees 
one into the other that it is impossible sharply to discriminate be- 
tween them. Surface clays are soft and unconsolidated, and are 
found at or near the natural surface. Shales are dense and rock-like; 
but are easily reduced to powder, and are readily worked into a 
plastic mass when mixed with water. Shale is often incorrectly 
called soapstone, from which it differs in nearly every respect. 
Shale is also frequently, but erroneously, called slate, from which 
it differs only shghtly in origin and composition; but slate, unlike 
shale, can not be rendered plastic by mixing it with water. The 
only method of distinguishing between shale and impure fire clay, 
except by a kiln test, is the fact that shale gives a conchoidal frac- 
ture while fire clay does not. 

924. Chemical Composition. It is not wise to enter into any 
extended consideration of the chemical composition of brick clays, 
since the subject is very comphcated, and since the engineer is 



476 BRICK PAVEMENTS [CHAP. XVII 

interested only in the physical properties of the finished product 
and should not attempt to prescribe the materials or to limit the 
methods employed by the manufacturer. 

925. Physical Properties. A chemical analysis of a clay may 
furnish sufficient evidence upon which to condemn it for brick- 
making purposes, but never enough for its indorsement. The 
following physical properties are important factors in determining 
the value of a brick clay: 1, its plasticity; 2, the amount of water 
required to make a plastic mass; 3, the amount of shrinkage, both 
in burning and in drying; 4, the rapidity of drying and also of burn- 
ing; 5, the temperature of incipient and complete vitrification; 
6, the density before and after burning; and 7, the strength of the 
burned brick. 

926. Manufacture of the Brick. Soft, homogeneous clay 
may be run through rollers, to crush the lumps, and from the crusher 
it may go directly to the moulding machine; but it is usually desirable 
to run it first through a pug mill, where it is mixed and worked 
with water into a plastic mass. Hard clays and shales are usually 
reduced to a powder in a dry pan, which consists of two heavy 
rollers or wheels running in a revolving pan having a perforated 
bottom. It is important to have the clay finely pulverized, because 
it will then fuse at a lower temperature, and also because fineness 
is necessary to the production of an even and close-grained texture 
which conduces to make the brick tough and impervious. The 
powdered clay is screened and then tempered with water in the pug 
mill or a wet pan. Fire clays are sometimes both crushed and 
tempered in a wet pan, which is similar to a dry pan except that 
the bottom is water tight. The wet pan gives better results than 
the pug mill, as the clay can be retained in the pan until it is thor- 
oughly tempered, but as it requires a large plant, and takes more 
labor and power, it is not usually employed in making paving brick. 
The more thoroughly the clay is worked or tempered, the more 
uniform and better will be the brick. 

927. Moulding. Paving brick are now made by the stiff-mud 
process. The moulding is done by an auger machine which forces 
the tempered clay or stiff mud through a die, thus giving a contin- 
uous bar of compressed clay. Fig. 164 shows an auger brick- 
moulding machine. At the right is the auger machine, in the 
middle the bar of clay, and at the left the cutting table or the 
machine for cutting the bar into bricks. 

Instead of an auger producing a continuous stream of clay, 



ART. 1] 



THE BRICK 



477 



reciprocating plungers are sometimes employed, which give an inter- 
mittent bar. The auger machine is the cheapest, and is ahnost uni- 
versally used. 

928. The weak point of the stiff-mud process is the laminations 
that must inevitably result from pushing a stream of clay through 
a fixed die. The friction of the sides of the die will cause differential 
speeds in the flow of the clay, and these variations must necessarily 
result in laminations in the clay bar. If the air has been expelled 




Fig. 164. — Auger Brick-moulding Machine. 



from the clay by the pug mill, these lines can be largely closed up 
again by a properly shaped die, and a first-class brick will result in 
which the laminations will be inconspicuous and of no importance; 
but if the air has not been expelled, or if the tapering former and 
the die are not properly designed, there will be a number of concentric 
lines that divide the cross section of the brick into a series of shells 
or concentric cylinders which greatly weaken the brick. These 
laminations vary with the character and the condition of the clay; 
and as a rule, the more plastic the clay the more prominent the 
laminations. 

929. Cutting the Brick. Formerly the size of the die was such 
as to give a bar of clay about 4^ by 2J inches, which the automatic 
machine cut into lengths of about 9J inches by forcing a wire through 
it, thus producing what is called an end-cut brick. But now the 
die is usually a httle greater than Sf by 4 inches, the excess depend- 
ing upon the shrinkage of the clay in drying and burning, and the 
bar is cut into sections 3J inches thick, thus producing a side-cut 
brick. Substantially all paving brick are now side-cut. 



478 



BRICK PAVEMENTS 



[CHAP. XVII 



930. Kinds of Brick. The first brick made especially for paving 
purposes was a square-edged side-cut brick with plane sides; but 
now several kinds or forms are in use. 

931. Re-pressed Brick. A re-pressed brick is one that after 
being moulded is subjected to a heavy pressure. The re-pressing 
makes the brick more symmetrical in form and of better appearance. 

In the early history of paving brick industry, it was claimed that 
one of the advantages of re-pressing was that it enabled the man- 
ufacturer to form grooves in the faces of the brick which facihtated 
the introduction of the joint filler and also increased the power of 
the filler to hold the brick in place in the pavement. Fig. 165 
shows three forms of grooved paving brick. 




Fig. 165. — Old-style Grooved Paving Bricks. 



The above form of brick proved undesirable, since the joints 
between the bricks when set or laid in the pavement were so narrow 
that it was difficult to get the filler into the joints. The demand 
next was for a brick having projections on the side which would 
automatically space the joints so they could be easily and com- 
pletely filled by the filler. In answer to this demand manufacturers 
formed lugs, or buttons, or raised letters on the side of a re- 
pressed brick, which served to keep the bricks a uniform distance 
apart and thus made joints into which the filler could easily be 
poured or swept. Fig. 166 shows re-pressed paving bricks which are 
much used. 

932. Even though re-pressed under a great total pressure, the re- 
pressing does not increase the density of the brick. In fact the re- 



ART. 1] THE BRICK 479 

press invariably increases the volume of the brick. The reasons 
for this are: 1. The box in which the brick is re-pressed must be 
slightly larger than the die-moulded clay block, so that the block 
can be easily dropped in; and hence re-pressing compresses the 
block in one direction, but expands it in the other two. 2. For 




Fig. 166. — Modeen Re-pkessed Paving Bricks, 

practical reasons the re-pressed block must have rounded edges; 
and the forming of the round edges disrupts the original structure 
and doubtless opens up some of the laminations. However, in 
1916, a few manufacturers began to make re-pressed brick with 
square edges. The practice seems to have been abandoned. 3. 
The formation of the lugs or buttons, or the making of the raised or 
sunken letters breaks the original bond of the clay and opens up the 
laminations. 

Experiments show that bricks not re-pressed are stronger and 
freer from structural defects than re-pressed brick. The cost of 
re-pressing is about 2 cents per square yard of pavement. There 
is little or no advantage to compensate for the decreased strength 
and increased cost due to re-pressing. 

933. A marked disadvantage of a re-pressed brick is that it has 
rounded edges, which makes it impossible to maintain the joint 
level full of filler. The filler chips out of such a joint much more 
easily than a joint between square-edged bricks. Re-pressed paving 
bricks were almost exclusively used for a quarter of a century. 

934. Wire-cut Lug Brick. In 1910 a method of cutting the bar 
of clay into bricks was introduced which gives a square-edged brick 
having on one of its faces four lugs integral with the body of the 
brick, and also having a groove adjacent to each lug. The lugs 
project YE of an inch, which insures a joint at least ye of 9>n inch 
wide; but in 1918 the lugs are to project only | of an inch, which 
will give a minimum joint of | inch. The brick also has a double 
bevel or bulge of ^ of an inch at each end, which insures an end 



480 



BRICK PAVEMENTS 



[chap. XVII 



joint at least y& of an inch wide at the top and bottom of the end 



joint. Fig. 167 shows this form of brick; 
brick laid in the pavement. 



and Fig. 168 shows such 




Fig. 167. — Wire-cut Lug Paving Brick. 




Fig. 168. — Wire-cut Lug Brick in Pavement. 



Fig. 169, page 481, shows the machine for cutting the bar of clay 
into wire-cut lug bricks. The clay is cut by forcing a wire horizon- 
tally through the bar, the wire being guided by narrow slots in 
plates above and below the clay. The slots on one side of the brick 
are wavy and form the lugs; while the slots on the other side are 
straight and form a plane surface. 

The advantages of the wire-cut lug brick are: 1. There are no 
laminations. 2. The lugs space the bricks when laid in the 



new 



pavement so as to make joints of uniform width and the beveled ends 



AUT. 1] 



THE BRICK 



481 



and the grooves on the vertical faces make it easy to jBU the joints 
completely. 3. The square edge of the brick makes a joint that 
holds the filler better than the round-edge of the re-pressed brick, 
since the filler does not feather out at its wearing surface. 4. The 
wire-cut face is rougher than the smooth face of the re-pressed bricks, 
and therefore the joint filler adheres better.* 




Fig. 169. — Machine for Cuttiiig Wike-cut Lug Brick. 

On the other hand, the wire-cut lug bricks require considerably 
more filler than the re-pressed brick. 

The wire-cut lug brick is patented; but many manufacturers 
are licensed to make it, and it is sold in unrestricted competition. 
Something like three fourths of all the paving bricks used east of 
the Mississippi river are of this type. Many manufacturers make 
both the wire-cut lug and the re-pressed paving brick. 

935. Vertical-fiber Brick. The vertical-fiber brick is one cut 
from a die-moulded bar of clay by wires travehng in straight par- 
allel slots, which is laid in the pavement with the wire-cut face up, 
and hence the wear comes upon the end of the laminations or fibers. 
Lugs are formed on one side of the brick by notches or grooves in 
one side of the die. Apparently this form of brick is made only by 
members of the Western Paving Brick Manufacturers Association, 
and promoted by it. 

The advantages officially claimed for this type of brick are: 1. 



* For experimental data proving this, see Engineering Record, Vol. 69 (1914), p. 607. 



482 BRICK PAVEMENTS [CHAP. XVH 

It is not patented, and therefore can be made by any manufacturer 
without paying royalty. 2. The depth of the brick as laid in the' 
pavement can easily be changed by simply changing the spacing of 
the cutting wires. 3. The brick can be set in the kiln so that all 
kiln marks come upon the vertical surfaces, and hence leaves the 
bedding and wearing faces free from such marks and makes a smoother 
pavement. 4. In the vertical-fiber brick the wear comes upon the 
end of the laminations, instead of on the sides as in other kinds. 
5. The wire-cut surface gives a good foothold for horses. 6. If a 
bituminous fiUer is used, the wire-cut surface aids in retaining a 
carpet of bituminous material on the surface. 

Of the above claims 1, 2, 3, and 4 must be admitted as being true; 
but there is a great difference of opinion as to the importance of the 
advantage claimed. Claim 5 is of doubtful value, since aU brick 
pavements afford a satisfactory foothold for horses. Claim 6 is a 
disadvantage rather than an advantage, since the smoother the sur- 
face of a brick pavement the better, and since at best a thin film of 
bituminous cement can not endure long on a brick pavement (see 
§ 579). It is a reversal of good practice to place the rougher face 
horizontal and the smoother vertical. 

The weight given to the above claims seems to be largely a matter 
of locality. The wire-cut lug brick is favored by at least most of the 
members of the National Paving Brick Manufacturers Association, 
while the vertical-fiber brick seems to be preferred by the members 
of the Western Paving Brick Manufacturers Association. The ter- 
ritory of the former is east of the Mississippi river, and that of the 
latter west of that river. However, as only about 4 per cent of the 
paving bricks made in the United States are manufactured between 
the Mississippi river and the Rocky Mountains, this difference of 
opinion is not important. Many re-pressed and wire-cut lug bricks 
are used west of the Mississippi river. 

936. Hill-side Brick. To afford a better foothold for horses on 
steep grades, a special hillside brick is made. There are two forms: 

1. A brick laid with its long dimension across the street and hav- 
ing one edge each of its top and bottom edges chamfered, which gives 
a series of continuous parallel grooves running transversely across 
the road or street. These bricks are usually re-pressed, the cham- 
fered corners being produced by filUng up opposite edges of the 

mould. 

2. A brick laid with its long dimension lengthwise of the road 
or street, and having one or more transverse grooves on each of 



ART. 1] 



THE BRICK 



483 



its two edges, thus producing a series of non-continuous parallel 
grooves across the road. These brick are die-moulded side-cut, 
the grooves being produced by 
metal lugs on the sides of the die. 
Fig. 170 shows a wire-cut lug hill- 
side paving brick; and Fig. 171 
shows such brick in the pave- 
ment before rolling and before 
the application of the joint filler. 
Fig. 171 is a street in Toronto, 
Canada, on a 6 per cent grade. 
Sometimes a strip of hill-side 
bricks is laid on each side of the 
street with a strip of ordinary 
paving bricks in the center. 

937. After being moulded, or 
after being re-pressed, the bricks 
are placed on trucks or cars, 
and conveyed to the dry house. 

A paving brick immediately after being moulded contains 20 to 30 
per cent of water; and hence thorough drying greatly faciUtates 
the burning of the brick. 




Fig. 170. — Wire-cut Lug Hill-side Paving 
Bkick. 




Fig. 171. — HilltSide Brick in a Pavement. 



938. Burning. Paving bricks are usually burned in down-draft 
brick-ovens having fire pockets or furnaces built in their outer walls. 



484 BRICK PAVEMENTS [cHAP. XVlI 

The bottoms of the kilns are perforated to allow the gases to pass 
through the flues, which are beneath the floor, and which lead to the 
chimney. The fire passes up from the furnaces into the kiln, then 
down through the brick to be burned to the flues, and thence to the 
chimney. The burning is the most critical step in the manufacture 
of paving brick. At first the heat is applied slowly in order to drive 
off the remaining water without cracking the brick. A low heat is 
continued until the smoke passing off shows no further signs of steam 
or '' water-smoke," after which the fires are gradually increased 
until the temperature throughout the kiln is sufficient to vitrify the 
brick. Most shales vitrify at from 1,500° to 2,000° F.; but impure 
fire-clays require from 1,800° to 2,300° F. From seven to ten days 
are required to raise the entire kiln to the vitrifying temperature. 

There has been much discussion as to the meaning of the term 
vitrification as applied to brick making. Literally speaking, to 
vitrify means to render glassy; but as applied to clay working, 
vitrification has come to mean incipient fusion of th§ particles of 
the clay into a new chemical compound. The degree of vitrification 
increases with the temperature, and the logical end of the process 
is complete fusion. A clay is partially vitrified if its constituents 
have begun to unite by heat into a compound silicate, even though 
it may not have a glassy fracture. The physical peculiarities which 
mark vitrification in a burned clay are the conchoidal fracture, the 
absence of pores, and the blending of the ingredients into one mass. 
Cracks, fissures, and cavities may be found, but porosity must not 
exist in a well vitrified brick; and the original particles must have 
begun to cohere by the bond of heat instead of the bond of plas- 
ticity. Within limits which are different for different clays, the 
degree of vitrification in a burned clay is measured by its ability to 
absorb water. A Hghtly burned brick will greedily absorb water, 
and the greater the degree of vitrification the less the water absorbed, 
a fully vitrified brick absorbing absolutely no water. 

After the bricks have been vitrified entirely through, the kiln is 
tightly closed and allowed to cool very slowly. Rapid cooling 
renders the brick brittle; but by slow cooling they are annealed and 
rendered tough. Slow cooling is the secret of toughness, and the 
slower the cooling the tougher the brick. The annealing is fre- 
quently unduly hurried, much to the detriment of the toughness 
of the brick. The kiln is often cooled in three to five days, when 
seven to ten would materially improve the product and usually 
would be worth the extra cost. 



ART. 1] THE BRICK 485 

With the utmost care a considerable per cent of the contents of 
the kiln are unsuitable for paving purposes, because of some being 
under-burned and some over-burned. With shale 80 to 90 per cent 
of first-class paving brick is a high average, while with impure fire 
clay 85 to 90 per cent may be produced. 

939. Size of the Brick. Formerly there was considerable differ- 
ence of opinion as to the best size for paving brick, some advocating 
2iX4X8^ others 3iX4X8j'', and a few 4X5X12''. The first 
size is always referred to as a brick, but the last two are sometimes 
called paving blocks. The last was never made in any quantity, 
and has been entirely abandoned. There is no conventional line by 
which to distinguish bricks from blocks. It was often claimed that 
one or the other size made the better pavement, but there is no 
material difference in the quality of the pavement between the dif- 
ferent sizes. 

The advantages of the building-brick size are: (1) being smaller 
they are more easily vitrified, and therefore a little cheaper to man- 
ufacture; and (2) brick unsuitable for use in the pavement can be 
more readily disposed of for building purposes, a fact which tends to 
cheapen the cost of the brick used in the pavement. The advan- 
tages of the block-size to the manufacturer are that there are fewer 
pieces to handle; and in the pavement the blocks chip or spall on 
the edges less than the bricks, particularly if the filler is not rigid 
(see § 1014). The manufacturer of the block sometimes places 
building brick in that part of the kiln in which it is difficult to burn . 
blocks thoroughly (the bottom of a down-draft kiln), a process which 
decreases the per cent of blocks unsuitable for paving purposes, and 
at least partially eliminates the second advantage of the building- 
brick size as above. In the early history of brick paving, bricks 
were most in favor; but now the blocks are used ahnost exclusively, 
and usually they are called bricks. 

940. Uniformity of size is very desirable to prevent confusion in 
buying and bidding, and particularly for convenience in making 
repairs. Unfortunately the sizes of building bricks and also of paving 
bricks or blocks vary considerably in different parts of the country. 

941. The Specifications of the National Paving Brick Manu- 
facturers Association, which have been widely adopted by engineers, 
prescribe re-pressed and wire-cut lug paving blocks shall be 8J 
inches long, 4 inches deep, and 3| inches wide, with the provision 
that shallower brick may be used (see § 942). The specifica- 
tions of the Western Paving Brick Manufacturers Association seem 



486 BRICK PAVEMENTS 



CHAP. XVII 



to have no standard size for vertical-fiber brick; but seem to make 
such brick from 3f to 4| inches wide, from 8 to 9 inches long, and 
2i, 3 or 4 inches deep, a depth of 2| inches seeming to be the 
most common. 

Until 1916 the Specifications for Brick Pavements adopted by 
the American Society of Municipal Improvements permitted the 
use of either bricks or blocks; but in 1916 the specifications were 
amended so as to permit the use of only blocks 8| inches long, 4 
inches deep, and SJ inches wide. 

The width is always exclusive of lugs or buttons. 

942. Thus far in the history of brick pavements, the depth of 
the brick has quite uniformly been 4 inches; but some engineers 
claim that no brick pavement ever failed through the wear on the 
brick, and therefore the depth of the brick should be reduced. 

In 1915 a nev/ type of brick pavement was introduced (§ 982), 
which would safely permit a reduction in the total thickness of the 
pavement. This and relative matters are discussed in § 1028. 

943. Testing the Brick. It is important to have a definite 
method of testing the quahties of any artificial material, since then 
all parties may know exactly the grade called for, and since the 
results obtained by different observers with different materials may 
be compared. This is particularly true of brick, since the clays 
differ greatly in quality, and also since a shght variation in each step 
of the manufacture materially affects the result. The object of 
testing paving brick is two-fold: (1) to determine whether the mate- 
rial is suitable for use in a pavement; and (2) to enable comparisons 
to be made between different classes of brick. 

Several tests formerly employed have now been practically 
abandoned; but for the sake of completeness these will be briefly 
considered. 

944. General Appearance. A critical examination of a paving 
brick by the experienced eye aided by a hand hammer is a fair method 
of determining the relative merits of different bricks of a particular 
kind; but unfortunately experience with one make is not of much 
value with brick made by a different process or of a different kind of 
clay, and further the results by this method of testing admit of no 
numerical evaluation or even of being described accurately. It is a 
method of selecting or inspecting rather than of testing. 

The brick should be reasonably straight; and have flat sides and 
square corners; be uniform in size, texture and shape; and be hard, 
tough, and evenly burned. If the edges of the bricks are square, 



ART. 1] THE BRICK 487 

they should be smooth and free from serrations or " ragging," due 
to friction in the die. If the edges are rounded, the radius should 
not exceed three sixteenths of an inch. Kiln marks or impressions 
from the over-lying brick in the kiln must not be more than three 
sixteenths of an inch deep. One face should have not less than two 
nor more than four projections, which should be not more than one 
fourth nor less than one eighth inch high, nor exceed one half square 
inch in area. 

When broken the interior of the brick should show a uniform 
fracture, be free from hme, and contain no uncrushed or lumpy 
material, especially if such material is not united by vitrification 
with the remainder of the material. There should be no marked 
laminations. 

945. Size. The brick should closely conform to the standard 
size (§ 941) or to the specified size. The brick from any one man- 
ufacturer should be of uniform size; and the brick for any one job 
should be of practically the same size. The usual specifications are 
as follows: ''A brick shall not vary from standard or specified 
dimensions more than | an inch in length, nor more than | inch in 
width or depth." Sometimes it is also specified that " the bricks 
in any one shipment must not vary in width or depth more than 
I of an inch." 

946. Color. The color is no criterion of the value of a paving 
brick, when comparing bricks of various makes; but, in inspecting 
bricks from a single factory, the color v/ill usually furnish a fairly 
safe guide as to the relative hardness, when the inspector is thor- 
oughly acquainted with the particular manufacture. The knowl- 
edge gained regarding the relation of color and quality in inspecting 
one make of brick, however, can seldom be used with that of another 
make from a different locality, as clays vary greatly in kind and 
degree of color. The popular behef is that hardness is proportional 
to the darkness of the color of the brick, and that hght color is prima 
facie evidence of softness. As a rule the impure fire clays make 
excellent paving material, although the bricks are light colored, 
usually buff, while shale bricks are red or brown. For a particular 
clay, the color of the bricks indicates the degree of heat they have 
received, provided they were burned with the same fuel and under 
the same conditions; and ordinarily the higher the heat the darker 
the color, and presumably the better the brick. The imiformity 
of the color of the interior of the brick is more important than the 
color of the exterior. 



488 BRICK PAVEMENTS [CHAP. XVII 

The color of the outside of the brick is sometimes valueless 
owing to the sand employed to prevent sticking in the kiln, or to 
the effect of sulphur in the coal used in burning, or to salt glazing. 
Salt glazing is a trick occasionally employed to give a dark gloss to 
the outside which is very attractive to the superficial observer, 
but which is practically worthless, since it is only skin deep and 
soon wears off. Salt glazing makes it more difficult to detect soft 
brick, and should never be allowed on paving brick. 

947. Specific Gravity. In a general way, the more dense a brick 
the harder and stronger it is; and consequently early in the history 
of brick testing it was believed that a knowledge of the specific 
gravity would be of value in judging of the quality of a paving 
brick. It is now known that the specific gravity reveals nothing 
not determined by other tests; and further that the density depends 
upon the character of the clay, the kind of fuel, etc., and in no way 
measures the quality of the product. The specific gravity may be 
computed by the formula: 

Specific gravity = ^^J"^., 

in which Wa represents the weight of the dry brick in air, Ws the 
weight of the saturated brick in air, Wi the weight of the brick 
immersed in water. The specific gravity of shale brick ranges 
from 2.05 to 2.55, and usually from 2.20 to 2.40; and that of brick 
made from impure fire clay ranges from 1.95 to 2.30, and generally 
from 2.10 to 2.25. 

948. Crushing Strength. The results for the crushing strength 
vary more with the details of the method employed than any other 
test of paving brick. There is no standard method of making this 
test. For experimental data showing the marked effect of the dif- 
ferent methods of testing, see the author's Treatise on Masonry 
Construction, tenth edition, § 10-17, and § 78-81. 

Tests on cubes cut from paving brick show that the best paving 
brick have a crushing strength of 10,000 to 20,000 lb. per square 
inch. This is the crushing strength when the load is apphed uni- 
formly over the surface of the test specimen; but if the pressure is 
applied to only a small part of the upper surface of a brick, the 
strength will be much greater.* Any brick that is likely to be 

* See Baker's Masonry Construction, tenth edition, § 657. 



AET. 1] THE BRICK 489 

accepted for paving purposes by any of the tests hereafter described, 
is in no danger of being crushed by the pressure of the wheel of a 
vehicle. For example, the surface of contact between a wheel 
having a Ij-inch tire loaded with half a ton is about one half square 
inch, which gives a pressure on the brick of only about 2,000 lb. 
per square inch. 

If the crushing strength could be easily and accurately found, 
it would be of value in determining the relative strength, and hence 
would be useful in comparing the quality of different brick; but 
owing to the difficulty of making the experiments and to the uncer- 
tainty of the results, the test has been abandoned. 

949. Absorption Test. In the early days of the paving brick 
industry, many of the brick used were so porous and brittle that it 
was feared they would be disintegrated by the action of frost; and 
consequently the absorption test was employed to eliminate porous 
brick. Subsequent tests by repeatedly freezing and thawing paving 
bricks showed that any brick which was likely to be accepted for 
paving purposes would not be appreciably injured by the action 
of frost. There are probably two elements that prevent frost from 
seriously injuring even a soft paving brick; viz.: (1) the cushion- 
ing effect of the air remaining in the pores of the brick, and (2) the 
strength of the brick may be greater than the disrupting effect of 
the frost. Alternate freezing and thawing might injure a non- 
vitrified brick, which is not only very porous but is also deficient in 
strength; but such a brick would be rejected for paving purposes 
as the result of a casual inspection. The absorption test is no 
longer regarded of importance as measuring the ability of the brick 
to resist freezing and thawing. 

Different bricks vary widely in their rate of absorption. For 
example, one brick absorbed in one day 80 per cent of its total 
amount, while another absorbed only 8.7 per cent; and two other 
specimens absorbed 71.8 and 19.5 per cent respectively in the same 
time. The absorption of whole brick is slightly less than that of 
half brick, and the absorption of half brick is considerably less 
than that of small chips. For the above reasons and for other 
minor ones, results for the absorptive power are likely to be untrust- 
worthy. 

950. Transverse Strength. This is determined by resting the 
brick upon two knife-edges and applying a steady pressure on the 
upper side of the brick through a third knife-edge placed midway 
between the other two. The results are expressed in terms of the 



490 BRICK PAVEMENTS [CHAP. XVII 

modulus of rupture, which is computed by the following formula: 

SWl 



R = 



2hd?' 



in which R represents the modulus of rupture in pounds per square 
inch, W the breaking load in pounds, I the distance between sup- 
ports in inches, h the breadth of the brick in inches, and d the depth 
of the brick in inches. The brick may be tested edgewise or flat- 
wise, although the former is usually the better method, since then 
W is larger. The knife-edges should be rounded transversely to 
a radius of about one sixteenth of an inch and longitudinally to a 
radius of about 12 inches, to secure better contact and to prevent 
the brick from being crushed at the edges. Some authorities rec- 
ommend grinding opposite edges of the brick to parallel planes, 
but this is a useless expense. If the brick is warped, the contact 
between the brick and the knife-edges can easily be made entirely 
satisfactory by placing pieces of metal under the blocks carrying 
the lower knife-edges, or by shifting the brick longitudinally, or by 
turning it. 

The modulus of rupture of bricks that have given excellent 
service in a pavement varies from 1,500 to 3,500 lb. per square inch, 
usually from 2,000 to 3,000. Owing to apparently unavoidable 
variations in the structure of the brick, it is not possible to attain 
closely concordant results in making this test; and with the utmost 
care in selecting the brick and in making the tests, the variation 
from the mean ranges from 8 to 30 per cent, and on the average is 
about 20 per cent. 

The cross-breaking test furnishes a means of comparing the 
toughness of various kinds of paving brick. The uniformity of 
the results for any particular kind of brick indicates its structural 
soundness, freedom from air checks, etc., and shows whether the 
material has been properly treated in the various stages of manu- 
facture. The transverse strength indicates the resistance of the 
brick to cross breaking when laid in the pavement on an unyield- 
ing and uneven surface; but this element is not entitled to much 
consideration, since brick are seldom thus broken in the pave- 
ment, at least not until nearly worn out. 

The test is comparatively easy ^ to make, and is a valuable check 
upon the rattler test (§ 951). 

951. Rattler Test. This test is made by rolling or tumbhng the 
bricks in a foundry rattler, i. e., a revolving cast-iron barrel; and it 



ART. 1] THE BRICK 491 

greatly exceeds in importance all the other tests combined. It 
imitates more closely than any other, the impact due to the horse's 
hoofs and shoes, and to the bumping of the vehicle wheels, and also 
the abrasion due to the shpping of the horse's feet and the sliding 
of the wheels. This test could with propriety be called an impact 
and abrasion test. The result of the test is jointly dependent upon 
the toughness of the brick — its abihty to resist shock, — and its 
hardness — ^its ability to resist abrasion. 

To make this test of any scientific value, it is necessary to have 
some standard method of conducting the experiments. Several 
methods of standardizing this test have been proposed. The first 
test was made by the author. * Brick that had seen service in a pave- 
ment and pieces of well-known natural stones used for paving pur- 
poses, together with small pieces of scrap cast iron, were rolled in a 
rattler. Shortly after being proposed, this method was quite widely 
adopted; but it did not give satisfactory results, chiefly because the 
original experiments were made with a rattler having wooden staves, 
while subsequent tests were made with rattlers having cast-iron 
staves. The method was objectionable on account of the trouble 
and expense of preparing the test pieces of natural stone. Later 
each of four radical modifications of the test gained prominence in 
succession for a time. Finally it was found that seemingly unim- 
portant details materially affected the results, as, for example, the 
chemical composition of the cast iron in the staves and abrading 
material, the stiffness of the staves, the frequency of renewal of the 
staves and abrading material, the speed of rotation, the method of 
driving the rattler, etc. 

952. In 1910 after a very elaborate series of tests, the National 
Paving Brick Manufacturers Association proposed specifications 
which set forth in great detail the method of constructing and using 
the rattler; and in 1915 substantially these specifications were 
adopted by the American Society for Testing Materials, and they 
have been generally accepted as the standard, f 

Fig. 172, page 492, shows the standard rattler and abrasive mate- 
rial. The latter consists of two sizes of cast iron spheres, the larger 
weighing 7.5 lb. each and the smaller 0.95 lb. The total abrasive 

* Durability of Paving Brick, by Ira O. Baker, pp. 46, 5" X 8". T. A. Randall & Co., 
Indianapolis, Ind., 1891. Out of Print. 

t Proc. Amer. Soc. for Testing Materials, Vol. XV, Year Book 1915, Report of Committee 
C-3, pp. 396-407. Copies of complete specifications for the inspection and testing of paving 
brick may be had by addressing Secretary Amer. Soc. for Testing Materials, Philadelphia. Pa., 
or Secretary National Paving Brick Mfrs. Assoc, Cleveland, Ohio. 



492 



BRICK PAVEMENTS 



CHAP. XVII 



charge consists of 10 large spheres and 245 to 260 small ones, the 
collective weight being as nearly as possible 300 lb. 




Fig. 172. — StandarC Brick Rattler. 

In consulting the literature concerning tests of paving brick, 
it is necessary to carefully distinguish between the present and the 
former standard. The latter gives the smaller loss. 

953. Making the Test. To make the rattler test, the bricks are 
thoroughly dried, weighed, placed in the rattler, and turned 1,800 
revolutions at a speed of 30 revolutions per minute, and then 
weighed. The percentage of loss indicates the quahty of the brick. 

Fig. 173 shows the brick charge before and after testing. Ten 
brick of the so-called block-size constitute a charge. 

954. The object of the rattler test is twofold, viz. : (1) to deter- 
mine whether the bricks are tough enough for use in a pavement, 
and (2) to determine whether the material is uniform in quahty. 
The first is determined by the average loss of a charge, and the sec- 
ond by the uniformity of loss of the several bricks. Uniformity 
of wear is an important quality, for a single soft brick may wear 
so as to make a hole in the pavement, and then each passing wheel 
will rapidly destroy adjacent bricks even though they themselves 
are of excellent quality. 

To determine the uniformity of wear, the rattler test should be 



ART. 1] 



THE BRICK 



493 



SO conducted as to find the loss of each brick. This requires the 
marking of the bricks so they can be identified after being tested. 



I 



.,^^. 



# 



Pi— ^ 





Fig. 173. — Brick Charge before and after Testing. 

955. Marking the Brick. There are several schemes in use for 
marking the several bricks of a charge. 

The following method is used by William H. Howell, Engineer 
of Streets and Highways, Newark, N. J.* "The holes may be 
made with a small cold chisel, after a little experience, in twenty 
to twenty-five minutes." Fifteen holes are required. 

1. One drill hole on one side. 

2. One drill hole on one edge. 

3. One drill hole on each side. 

4. One drill hole on each edge. 

5. One drill hole on one end. 

6. One drill hole on each end. 

7. Two drill holes on one side. 

8. Two drill holes on one edge. 

9. One drill hole each on one edge and one end. 
10. Blank. 

The method shown graphically in Fig. 174, page 494, was pro- 
posed by C. A. Baughman, Instructor in Civil Engineering, Iowa 
State College. t The holes are made with a small diamond drill, 



* Proc. Amer. Soc. of Municipal Improvements, 1911, p. 95. 
t Engineering and Contracting, Vol. 44 (1915), p. 470. 



494 



BRICK PAVEMENTS 



[CHAP. XVII 



and are about one eighth of an inch deep. Eighteen holes are 
required. 



e 7 

oNearJ/de 



o 




o 




o o 




o @ 




o © 


/ 




^ 




3 




4 




5: 


• 




o o 




• 




O O 




o o 



(9 



9 10 

%BofhJ/de^ 



Fig. 174. — Battghman's Method of Maeking Brick. 



Fig. 175 shows the method proposed by Mr. B. L. Bowling, 
Assistant in Road Laboratory, University of Illinois, for marking 
wire-cut lug brick. Brick No. 10 is not marked. Notice that only 
nine holes are required. The holes are one fourth of an inch in 
diameter, and one fourth of an inch deep; and can be made with a 
compressed-air percussion drill in about forty minutes. 



Lug J/de 



r/at J/de 



Edge 



J 



E 



e 



Fig. 175. — Bowling's Method of Marking Wire-cut Lug Brick. 



Of course, determining the loss of each brick in the charge re- 
quires extra time in marking and weighing; but it is believed that 
the additional cost is abundantly justified. It is sometimes claimed 
that the brick can not be marked so as to identify them after the 
test without weakening them and increasing the loss in the rattler; 



ART. 1] THE BRICK 495 

but it has been proved that this is not true to an appreciable extent 
in any of the three methods of marking mentioned above. 

956. Limit of Loss, The standard specifications do not pre- 
scribe any hmit for the permissible loss; but distinctly state that 
such hmit shall be determined by the contracting parties. The 
standard specifications give " the following scale of losses to show 
what may be expected of tests executed under the foregoing speci- 
fications : 

For bricks suitable for heavy traffic 22 to 24 per cent. 

For bricks suitable for medium traffic 24 to 26 per cent. 

For bricks suitable for light traffic 26 to 28 per cent. 

"Which of these grades should be specified in any given district and for any 
given purpose, is a matter wholly within the province of the buyer; and should be 
governed by the kind and amount of traffic to be carried, and the quahty of paving 
bricks available." 

957. The Hmit that should be specified for the average loss in 
any particular case will depend upon the following: (1) the traffic 
to be carried, (2) the ordinary quality of the brick available, (3) 
the expense to be incurred in culling or selecting the brick, (4) the 
size of the brick or block, (5) the form of the edge of the brick, (6) 
the minimum dimension of the brick, (7) the uniformity of the loss. 

1. The amount and character of the travel may be such as to 
make it unwise to specify the highest grade of brick. 

2. The locality may be such that the ordinary paving bricks are of 
a high quality, and hence no appreciable increase of expense will be 
incurred by requiring a high grade of brick, i. e., a low rattler loss. 
For example, in a certain year the average loss of all the bricks sub- 
mitted to a testing laboratory in an eastern state was 18 per cent, 
and several lots of each of three brands gave an average loss of 
only 14.3 per cent; but on the other hand, all the bricks submitted 
in a year to a laboratory in a western state gave an average loss of 
22.56 per cent, with only three charges having a loss less than 17 
per cent. In some localities, specifying a small loss may Hmit 
competition and thus increase the price of the bricks. 

3. If the bricks available are not uniformly good, and if the 
service required of the proposed pavement is severe, it may be wise 
to specify a quality which will require careful selection and possibly 
include only a comparatively small percentage of the kiln run. Of 
course, the last method is expensive, because of the cost of culling, 
and also because the better bricks should bear part of the possible 
loss on the rejected bricks. 



496 BRICK PAVEMENTS [CHAP. XVII 

4. The limit to be set for the loss depends upon the size of the 
bricks or blocks, i. e., whether the pavement is to be built of bricks 
or blocks. However, as but few bricks are now used in pavements, 
this phase of the subject is not important. Apparently the relative 
loss of bricks and blocks has not been determined with the 1910 
standard rattler; but in view of data obtained with the former 
standard, some authorities permit a differential of 2 per cent in favor 
of brick in comparison with block. 

5. The Hmit varies also with the form of the edge or corner of 
the brick. If a brick has square corners, it will lose more in the 
rattler than one having rounded corners. The standard re-pressed 
brick has corners of a j^-inch radius, and the absent corner represents 
about If per cent of the volume. Therefore a square-cornered 
brick could lose If per cent in the rattler before being on a par with 
a standard round-edge re-pressed brick. For this reason, some 
claim that the former should be allowed 1 or 2 per cent greater 
rattler loss than the latter. The Illinois Highway Commission 
allows the standard wire-cut lug brick a differential of 1 per cent 
over the standard re-pressed brick. 

6. The hmit should depend upon the minimum dimension of the 
brick. Since the general use of a concrete foundation for brick 
pavements, and particularly since the introduction of the semi- 
monolithic and the monolithic construction, there has been a marked 
tendency to use a shallower brick. Formerly paving brick were 
quite uniformly 4 inches deep; but now, bricks of various depths 
are being used, SJ, 3, 2 J inches (§ 1028). The prescribed Hmit of 
rattler loss should be less the thinner the brick. The loss in the 
rattler is mainly due to the edges being worn or broken off (Fig. 
173, page 493). The central portion of a brick loses almost nothing 
except at its edges or corners. A brick 3^X4X8^ inches has 64 
inches of edges or corners, while a brick 3i X3 X8| inches has only 
60 inches of edges, or 6i per cent less. Apparently then for this 
reason a difference should be made in the limiting loss between a 
4-inch and a 3-inch brick. Further, it is clairaed that the form of 
the rattler test is unjust to a brick thinner than the 3|X4 X8i-inch 
standard, since if a thin brick becomes bridged in the rattler it is 
much more hkely to be broken than a thicker one. The Ohio High- 
way Department takes account of these two factors, at least 
approximately, as follows: It specifies a loss for standard 4-inch 
brick of not more than 22 per cent, and then inserts the following 
clause in its standard specifications: '' If other than standard sized 



ART. 1] THE BRICK 497 

blocks are required by the plans or specifications, the average rattler 
loss allowed shall be 22 per cent multiplied by the ratio of the volume 
of the standard block to the volume of the block specified, less 2 
per cent." For another method of testing 3-inch brick, see the 
second paragraph of § 960. 

7. The limit depends also upon the uniformity of loss of the sev- 
eral bricks of a charge. A low rattler loss with a wide range will 
probably not give as durable a pavement as a larger average loss 
with a narrower range. A single soft or brittle brick will soon wear 
below those adjacent to it, and then each passing wheel, particularly 
a steel-tired one, in dropping into the depression chips and crushes 
the adjoining bricks (however good they are) and tends to destroy 
the pavement. The Illinois State Highway Department recog- 
nizes this principle, and specifies that the average loss of wire-cut 
lug bricks may be 23 per cent provided the individual bricks have 
losses between 17 and 27, or 25 per cent provided the individual losses 
are between 20 and 28, or 27 per cent provided the individual losses 
are between 23 and 29. The degree of uniformity of the rattler loss 
depends upon the quahty of the bricks, but chiefly upon the care 
and skill employed in culling the brick at the kiln. For data on 
the degree of uniformity obtained in practice, see § 959. 

958. Loss Found in Laboratory. It is presumable that the pav- 
ing brick sent to a laboratory to be tested are usually samples pro- 
posed for use in a pavement; and hence the average losses are in- 
structive as showing the quahty of the material available in that 
locality, and the range of loss in any charge is evidence of the skill 
employed in culling the brick at the kiln. Sometimes the sample 
may be sent to obtain for the manufacturer information concerning 
some point in manufacture; but usually the manufacturer will 
make such tests at home, and hence the samples tested at a pubhc 
laboratory may be considered fairly representative. However, 
the results obtained in any state or city laboratory will depend 
somewhat upon the maximum rattler loss permitted by the official 
specifications of that state or city. For example, if one state or city 
specifies a lower rattler loss than another state or city, manufac- 
turers when shipping brick for work under the former specifications 
are hkely to select a better quahty or cull the bricks more carefully 
than when shipping to the other state or city. 

In 1916 the Illinois Highway Department tested 59 charges of 
re-pressed blocks, which gave an average loss of 20.9 per cent; and 
71 charges of wire-cut lug brick, which gave an average loss of 19.9 



498 BRICK PAVEMENTS [CHAP. XVII 

per cent.* The three smallest losses for re-pressed brick were 16.8, 
16.8, and 17.0 per cent; and the three smallest for wire-cut lug brick 
were 17.4, 17.4, and 17.5 per cent. The three least ranges in loss of 
the individual bricks in a charge were: for re-pressed brick 3.5, 
3.8, and 3.8 per cent; and for wire-cut lug brick 4.0, 5.7, and 6.0 
per cent. The three greatest ranges in loss of individual bricks 
were: for re-pressed bricks 25.1, 27.8, and 31.1 per cent, and for wire- 
cut lug bricks 23.9, 24.1, and 26.2 per cent. The last results simply 
show that probably some of the samples were not carefully culled, 
although it is well known that it is sometimes practically impos- 
sible by appearance alone to eliminate all the poor brick. 

In 1916, Vermihon County, Illinois, tested 124 charges of blocks 
which were practically all wire-cut lug brick from a local plant. The 
average loss of all was 18.06 per cent. One charge had a loss be- 
tween 14 and 15 per cent, 7 between 15 and 16, 27 between 16 and 
17, 31 between 17 and 18, and 25 between 18 and 19. The average 
loss of the brick used in 8 miles of rural road was 17 J per cent. The 
range in the five best lots was 3.5, 3.7, 3.7, 4.1, and 4.3 per cent, and 
in the three worst was 21.1, 29.2, and 31.5 per cent.f 

The Iowa Engineering Experiment Station in 1916 tested 85 
different charges with an average loss of 22.56 per cent. The three 
smallest were: 16.31, 16.78, and 16.80. Twelve charges of re- 
pressed brick gave an average loss of 19.44; and 33 charges " that 
were not re-pressed '' gave an average loss of 24.06 per cent, and 
omitting four of the largest the average is 22.33 per cent. J The 
kind of brick in the remainder of the charges is not known; and the 
results for individual bricks are not known. 

In 1917 the Ohio Highway Commission tested 302 lots of 23 
different brands of blocks 4 inches deep, the average loss of all brands 
being 21.14 per cent. The three smallest average losses were 17.47, 
18.98, and 19.34; and the three largest were 23.95, 25.08, and 27.84. 
The range of average losses for the three brands having the smallest 
losses were respectively: 3.20 for four lots; 5.96 for 26 lots, and 
10.04 for 14 lots. Apparently, no results were obtained for individual 
bricks. § 

In one year the Maryland Roads Commission tested 19 charges of 
six different brands of blocks, the average being 18.7 per cent. Four 



* Data from F. L. Roman, Engineer of Tests. 

t Data from P. C. McArdle, Superintending Engineer, Danville, 111. 

t Data from R. W. Crum, in charge of testing. 

§ Data from A. S. Rea, Engineer ofl Tests. 



AET. 1] THE BRICK 499 

charges of one brand average 14.5 and three charges of another 14.3 
per cent. In another year the Commission tested 12 charges of one 
brand which averaged 20.83 per cent, one lot was rejected, and the 
average for the 11 lots accepted was 20.5 per cent.* 

The New York State Highway Commission in the past few years 
has tested many paving blocks, in one year making exactly 400 
diiphcate tests. For 1914-17 the average loss for wire-cut lug 
blocks was 21.3 per cent, and for re-pressed 20.9 per cent. The 
average loss in a duphcate test usually varied from about 17 to 24 
per cent, with a few as low as 15 and a few as high as 27 per cent.f 
In consideration of the way in which the samples were obtained it is 
not permissible to attempt to draw any conclusions from these data 
as to the relative quahty of re-pressed and wire-cut lug brick. The 
results seem to show a shght improvement in quality from year to 
year; and the results from several other laboratories agree with this 
conclusion. 

959. Loss Allowed in Practice. The classification of losses sug- 
gested by the American Society for Testing Materials is stated in 
§ 956. These hmits have been adopted by many cities. The rat- 
tler loss allowed by the IlHnois Division of Highways for wire-cut 
lug brick is stated in the previous section; and the permissible 
loss for round-edged re-pressed brick is 1 per cent less in each case. 

Vermilion County, Illinois, in 1916, built 8 miles of monolithic 
brick rural roads, and specified that the average loss of a charge 
should not exceed 23 per cent, and that no single brick should exceed 
27 per cent. The general average loss of the brick used was 17i 
per cent-t For a summary of all the rattler tests made, see the third 
paragraph of § 958. 

The Ohio Highway Department specifies that the average loss 
of standard brick shall not exceed 22 per cent; and that the range 
shall not exceed 8 per cent. For brick thinner than the standard, a 
differential is allowed as stated in paragraph 6 of § 957. 

The New York State Highway Department specifies a maximum 
average loss of 24 per cent. 

960. Changes in Test Proposed. In the early history of brick 
pavements the joints were usually filled with sand, and hence the 
wear of the brick in the pavement was due largely to impact; and 
therefore a form of rattler test was adopted in which the wear was 

* Data from H. G. Shirley, Chief Engineer. 

t Data from H. E. Breed, First Deputy Commissioner. 

t Engineering Record, Vol. 74 (1916), p. 678. 



500 BRICK PAVEMENTS [CHAP. XVII 

largely due to impact. But now the joints of brick pavements are 
usually filled with grout or at least a comparative hard bituminous 
cement; and hence the wear on the brick in the pavement is mainly 
abrasion. Therefore some engineers claim that the present standard 
rattler test does not reasonably well represent the conditions in the 
pavement. Consequently several changes have been proposed in 
the method of testing paving brick. 

The City of Baltimore has modified the standard rattler test 
bj^ leaving out the large balls and replacing them by an equal weight 
of the small spheres. This change was made because it was believed 
that the 7|-lb. spheres were unduly severe on brick thinner than 
the standard paving block. The City of Baltimore allows 3-inch 
brick when tested in this way a differential of IJ per cent over a 4- 
inch brick. This differential was arrived at by measuring the loss 
of the middle inch in a 4-inch brick, somewhat as described in para- 
graph 6 of § 957. This introduces a new method of testing, which 
is unfortunate since it makes confusion and limits comparisons. It 
is unfortunate that a differential for the 3-inch brick was not adopted 
for temporary use until the propriety of the present standard rattler- 
test for thinner brick could be fully investigated. Baltimore and 
the State Highway Departments of both New York and Pennsyl- 
vania are making comparative tests of 4-inch and 3-inch brick by this 
method; but at present there are insufficient data to warrant any 
definite conclusions. 

Some competent authorities claim most of the preceding diffi- 
culties would be met and more equitable results would be obtained, 
if the brick were tested by the standard rattler test using the same 
number of bricks regardless of their size, and were then compared 
by their absolute loss in weight rather than by the per cent of their 
losses. 

Attempts have been made to test paving brick by a sand blast;* 
but not much progress has been made. 

St. Louis has discarded the rattler test, and trusts to comparing 
the brick on the street with standard samples previously selected, t 
It has not been proved that this method is not subject to more 
objections than the rattler test. 

361. Service Tests. The relationship between the loss in 
the rattler and the service in the pavement has not been indi&put- 

* Trans. Am. Soc. Test. Mat., Vol. 16 (1914), Part II, p. 557-64; or an abstract of the same. 
Engineering Record, Vol. 70 (1914), p. 215. 
t Engineering Record, Vol. 72 (1915), p. 200, 



ART. 1] THE BRICK 501 

ably established. From time to time several experiments have 
been undertaken to determine the relative qualities of different 
grades of paving bricks by actual service in the pavement. The 
experiment consists in making a standard rattler test of different 
grades of paving blocks, and then laying short sections of pavement 
with each of the several kinds. For one reason or another, all of 
these experiments, except the one mentioned in § 962, have failed 
to give a conclusive result. 

For example, the first of these experimental sections was laid 
in May, 1898, in Detroit, Michigan. Transverse strips of fourteen 
kinds of brick were laid in a distance of 222 feet. The blocks were 
tested by a former N. B. M. A. standard rattler test. A comparison 
between the results of the rattler tests and a general observation of 
the effect of three years' wear in the pavement failed to show any 
close agreement between the rattler test and service in the pave- 
ment. But this test was not conclusive, because it was later found 
the rattler test used failed to discriminate between the good and the 
bad brick, and it was for this reason abandoned. 

962. In 1912-13 the Office of Pubhc Roads and Rural Engineering 
of the U. S. Department of Agriculture directed the construction 
of an experimental section of road upon an extension of Connecticut 
Avenue known as Kensington Road, near Chevy Chase, Maryland. 
The improvement was 6,195 feet long, and was divided into six 
sections each having a different road surface. Two sections had a 
surface of bituminous concrete, two oil-cement concrete, one hy- 
draulic-cement concrete, and one (the one nearest Chevy Chase) 
vitrified brick. The details of the design and construction of the 
several sections are described in the following publications : Circulars 
No. 98 and 99 of the Office of Pubhc Roads; Bulletins No. 105 
(1914), 257 (1915), and 407 (1916) of the U. S. Department of Agri- 
culture. Each year an examination is made of the condition of the 
several sections, and a report of the same is published ; and doubtless 
this practice will be continued for a number of years. A census 
of the travel on the road is taken for twentj^-four hours on every 
thirteenth day. 

The following are the particulars for the brick-paved section. 
The brick pavement is 18 feet wide, and 980 feet long. The con- 
crete base is 6 inches thick, and the proportions are 1:3:7, the 
coarse aggegate being gravel (pebbles). The bedding course is 2 
inches of sand. Fourteen varieties of paving blocks were laid. 
Table 55 shows the character of the blocks. The pavement 



502 



BRICK PAVEMENTS 



[chap. XVII 



was rolled with a 5-ton tandem roller; and then the joints were 
filled with a 1 : 1 portland-cement grout. The depth of the bricks 
constituting two courses of each variety were measured, and the 
location of these courses were recorded, so that in the future these 
brick may be taken up and measured, and the amount of wear thus 
be determined. The average traffic one-way on half of the road 
during 1915 consisted chiefly of 56 horse-drawn wagons and 342 
motor-driven cars. 

TABLE 55 
Characteristics of Paving Blocks on Chevy Chase Road 



Ref. 

No. 



1 

2 
3 
4 
5 
6 
7 
8 
9 
10 



12 
13 
14 



Description of Blocks. 



Shale wire-cut lug, hard burned 

" " " medium hard burned 

Shale, re-pressed, well vitrified 

'' " hard burned, coarsely ground 

" " very hard burned 

" " coarsely ground 

" " medium hard burned, even wear. . . . 

finely ground, 
coarsely " 
Fire-clay, re-pressed, medium hard burned, coarsely 

ground 

Fire-clay, repressed, soft burned, coarsely ground .... 

Shale, re-pressed, soft burned, coarsely ground 

Fire-clay, re-pressed, soft burned, finely ground 

" wire-cut lug, hard burned, laminated 



Absorp- 
tion — 

Average 
of Five 
Tests. 



1.39% 

1.31 

0.88 

1.65 

1.10 

1.81 

2.29 

3.74 

2.86 

1.56 
2.38 
4.04 
3.73 
3.68 



Loss in 
Rattler,— 
Average 
of Three 

Tests. 



21.12% 

16.36 

25.57* 

17.67 

22.04* 

18.80 

27.92t 

22.68 

22.59t 

19.11 

37.68t 
38.89t 
24.31t 
31.19 



* Loss due mainly to chipping. 



t Uniform. 



Three annual inspections have been made of the above sections 
of brick paving and each time the conclusion is that there is no 
appreciable difference in wear between the several varieties of brick. 
Apparently time enough has not elapsed to justify any trustworthy 
conclusion, since the wear has been so slight as to make it impossible 
to discover any difference between the different varieties of brick. 
It has been asserted that this experiment already proves that a 
brick having a large loss in the rattler wears as well as one having 
a much smaller loss; but this conclusion is not justifiable, since the 
wear on any brick is as yet exceedingly small, and the difference 
between different varieties is too small to warrant any conclusion 
as to relative wear. Doubtless in due time valuable information 
will be obtained as to the relation between the loss in the rattler and 
that in actual service. 



AET. 2] 



CONSTRUCTION 



503 



Art. 2. Construction 

963. Fig. 176, shows the several parts of a brick pavement of the 
standard type. 




Fig. 176. — Section of Brick Pavement with Sand Cushion and Conceete Foundation 



964. SUBGRADE. An essential feature in the construction of 
such a pavement is the proper preparation of the subgrade. It 
should be thoroughly underdrained, should be rolled until it is solidly 
compacted, and the surface should be smooth and of the correct 
crown and grade. 

Underdrainage has been fully discussed in § 113-24; and street 
drainage has been considered at length in Chapter XIII. The 
smoothing and roUing of the subgrade is considered in Art. 1 of 
Chapter XV. 

965. Foundation. In the evolution of the brick pavement 
several types of foundation were used for a time. 

966. Abandoned Types. The first brick pavement in this 
country, that at Charleston, W. Va., was laid on a foundation of 
1-inch tarred boards resting on a layer of 3 or 4 inches of sand, with 
a l|-inch sand cushion between the bricks and the boards. This 
form was not used to any considerable extent, and has been entirely 
abandoned. 

During the first ten or fifteen years after the introduction of 
brick pavements in the Middle West, the foundation consisted 
almost exclusively of a course of brick laid flatwise on a thin bed 



504 BRICK PAVEMENTS [cHAP. XVII 

of gravel or cinders. Such pavements are generally known as two- 
course brick pavements. The layer of cinders or gravel was leveled, 
and inferior paving brick were laid flatwise thereon; and then the 
joints of the bricks were swept full of sand. The chief defect in this 
form of foundation was that the joints of the lower course were not 
fully filled, and consequently after the pavement was in service the 
sand of the cushion coat (the layer between the two courses of brick) 
would work into these joints and permit the bricks in the wearing 
course to settle. To cheapen the pavement, broken and chipped 
brick were used in the lower course, and the tendency was to place 
the larger face uppermost, thus making it nearly impossible to fill 
entirely the joints during the time of construction. This form of 
foundation was abandoned on account of its cost and inferior 
quality. 

In some localities where gravel or broken stone was cheap, brick 
pavements were laid upon a layer of gravel or broken stone; but the 
difficulty and expense of getting such a foundation thoroughly com- 
pacted and properly shaped led to the substitution of a concrete 
foundation. 

In localities where the native soil is clean sand or fine gravel, 
brick pavements were constructed directly upon the natural soil. 
The subgrade is simply shaped and rolled. Quite a number of cities 
in the North, some of which have a considerable traffic, for example 
Cleveland, Ohio, and Galesburg, lUinois, and many cities in the 
South, lay such pavements on native sand. The sand is usually 
simply graded and puddled, the puddling being mainly to keep the 
subgrade hard and smooth until the bricks can be laid and the joints 
filled. Many southern cities lay brick pavements upon a 1-inch 
layer of cement mortar or fine concrete, this bedding course being 
used to prevent the sand subgrade from working up into the joints 
while the bricks are being rolled. Such foundations are wise only 
for light traffic streets, and the decreased cost of portland cement 
has led to the increasing use in such localities of a concrete founda- 
tion for even light traffic streets. 

967. Old Macadam Foundation. Not infrequently a brick pave- 
ment replaces a water-bound gravel or macadam surface, in which 
case it may be economical to use the old pavement for a founda- 
tion for the new. For a consideration of this case, see § 791 and 
§437. 

968. Bituminous Concrete Foundation. For a discussion of this 
type of foundation, see § 792-95. 



ART. 2] CONSTRUCTION 505 

969. Concrete Foundation. At present a layer of portland- 
cement concrete is the almost universal foundation for brick pave- 
ments. This form of foundation is fully considered in Art. 2 of 
Chapter XV — Pavement Foundations. 

970. Bedding Course. The bedding course is a layer of sand 
or mortar between the foundation and wearing coat to provide 
for slight variations in the surface of the foundation and small 
irregularities of size and form of the bricks. There are three dis- 
tinct forms of bedding layer, viz. : sand, a dry mixture of sand and 
cement, and wet mortar. 

971. Sand Bedding Course. The proper thickness of this layer 
will depend upon the regularity of the upper face of the concrete 
foundation and also upon the uniformity of the bricks in size and 
form. 

For reasons stated later (§ 977-78), the layer of sand should be as 
thin as will afford a good bed for the bricks; and therefore the top 
of the concrete foundation should be carefully finished with a surface 
parallel to the surface of the pavement. Not infrequently loose 
fragments of stone are left on the surface of the concrete, a result 
which is very undesirable, since they necessitate a thicker cushion 
and at best prevent the bricks from coming to a uniform bearing. 
With good workmanship in laying the concrete, there will be no loose 
pieces of stone on the surface; and if they do happen to get there, 
they should be removed before laying the cushion coat. 

The sand for the cushion should preferably be so fine as to be of a 
soft, velvety nature and should contain no pebbles of any consider- 
able size, or loam, or vegetable matter. The size of pebbles permis- 
sible depends upon the thickness of the sand bed. Pebbles will 
prevent the brick from having a uniform bearing; the loam is likely 
to be washed to the bottom of the layer and cause the brick to settle; 
while the vegetable matter will decay or wash away, and leave the 
bricks unsupported. The sand should be dry when it is spread. 
Even a small per cent of moisture in the sand adds considerably to 
its volume, particularly if it is fine; and hence if the sand when laid 
is wet and dry in spots, the cushion will not be of uniform thickness 
when dry. The shrinkage of the sand cushion away from the brick 
causes depressions which are unsightly, unpleasant to users of the 
pavement, and causes the pavement to wear more rapidly. Further, 
the shrinkage of the sand cushion away from the brick sometimes 
causes an unpleasant noise when vehicles pass rapidly over these 
spots (§ 1055). 



506 



BRICK PAVEMENTS 



[chap. XVII 



972. Spreading the Sand. The spreading of the sand should be 
carefully done, so as to secure a uniform thickness and to have its 
upper surface exactly parallel to the top of the finished pavement. 
After the sand has been distributed approximately to the proper 
thickness with a shovel, the surface should be leveled by drawing 
over it a template conforming exactly to the curvature of the cross 
section of the proposed surface of the pavement. 

Fig. 177 shows a common form of template, which was used in 
constructing a pavement 33 feet wide. It is trussed to prevent it 




Fig. 177. — Template for Striking the Sand Cushion. 



from sagging at the middle; and is also trussed to prevent it from 
deflecting toward either the front or rear. The template is pro- 
vided with two rollers at each end which run upon the top face of 
the concrete gutter. Some templates are provided with a roller 
upon a bent lever, by which the template can be lifted and rolled 
back. The length can be varied by means of fish-plates at each end; 
and the elevation of the cutting edge can be adjusted by the screw 
and hand-wheel at the left. 

Practice differs considerably as to the length of the template. 
Some contractors make the template the full width of the pavement, 
if that is less than about 30 feet, and for a wider pavement make the 
template half the width of the street. This form of template must 



ART. 2] CONSTRUCTION 507 

be made of a 2-inch pine plank of sufficient width to permit of the 
cutting of its lower edge to the proper curvature, which may be 
determined by the method explained in § 718 (page 374). If the 
template is long, it must be braced to prevent bending and sagging; 
and it must have a long and substantial handle at each end by which 
to draw it forward, and another handle at each end by which to carry 
it backward. It is desirable that the template shall have consider- 
able weight to keep it from hfting up as it is drawn forward; and 
when being drawn forward, the face of it should lean backward a 
little to keep it from lifting up. At each end there should be a roller 
or a metal runner to carry the template along the top of the curb or 
along the edge of the concrete gutter. The roller is more common, 
but the runner is better since it eliminates small irregularities in the 
top face of the forms, and also since it distributes the weight upon 
the forms over a longer length. If the template is to run on top of 
the curb, a roller also should be provided to keep it away from the 
curb. If the length of the template is equal to half the width of the 
street, one end of it may run upon a screed, or wood strip, equal in 
thickness to that of the cushion layer, placed in the center of the 
street. If there is a car track in the street, one end of the template 
may be made to run on the rail. 

A long template requires considerable force to draw it forward, 
and it is difficult to move backward. Some contractors, therefore, 
use a template equal to one quarter of the width of the pavement. 
For a pavement 30 to 40 feet wide, screeds made of 2-inch by 4-inch 
scantlings are placed at the crown, in the gutters, and also midway 
between the crown and the gutter, being bedded on a thin layer 
of sand so that their tops conform to the finished surface of the pro- 
posed sand cushion. The position of these screeds is determined by 
measuring down from a string stretched from curb to curb. The 
template may be made of a 1-inch by 6-inch plank, with a 1-inch by 
2-inch handle braced by two 1-inch by 2-inch pieces. The edge 
should be hollowed out to fit the curved surface of the pavement, 
although often this is not done. The middle ordinate for the curved 
cutting-edge of the template may be computed by the formula 

C d? 
m = -jz^, in which m is the middle ordinate in inches, C the crown 

of the pavement in inches, d half the length of the template in feet 
and D half the width of the pavement in feet. 

After the sand for the cushion layer has been distributed with 
shovels, the template should be drawn slowly over it several times, 



508 BRICK PAVEMENTS [CHAP. XVII 

any depressions that develop being filled by sprinkling sand into them 
with a shovel. A considerable quantity of sand should be drawn 
along in front of the template, as this aids materially in packing the 
bed. It is necessary to draw the template several times to pack the 
sand well, particularly if there are wet and dry spots, as the suc- 
cessive jarring of the sand grains causes them to settle more closely 
together. When the sand cushion is properly packed, it will have a 
uniform, smooth, velvety appearance, and will not look rough, 
porous, and grainy. No one should be allowed to step on the sand 
cushion after it has been spread, nor after it has been rolled. 

Formerly, when the concrete for the base was mixed by hand, 
the template was pulled forward entirely by men, or sometimes by 
one or two horses; but now it is moved forward, at least for the 
first trip, by hitching it to a self-propelling concrete mixer, or better 
by passing a rope over a winding drimi on the mixer. 

973. The surface of the cushion layer is sometimes prepared with 
a short lute or scraper without any screeds; but the template and 
screeds secure a more uniform surface and also give a greater com- 
pression and a more even bed. With hand luting the surface of the 
pavement is almost certain to be covered with saucer-like depressions 
after it has been rolled. Hand luting should be prohibited except 
where the use of the template is impossible, as at street intersections, 
around manhole covers, etc. 

A considerable part of the difference in tractive resistance between 
brick pavements No. 4 and Nos. 5 and 6 of Table 7, page 20, is due 
to the difference in the preparation of the sand cushion, the remainder 
of the difference being in the rolling of the brick (§ 991). 

974. In adjusting the thickness of the sand cushion adjoining 
concrete gutters, manholes, etc., care should be taken that the upper 
surface of the brick after being rolled is not below the upper face of 
the gutter. 

975. After the sand cushion has been struck off with the tem- 
plate, it should be rolled with a hand roller about 30 inches long, 
24 inches in diameter, and giving a pressure of about 15 lb. per 
linear inch. An ordinary two-section lawn mower with a 12-foot 
handle is satisfactory for this work. 

A 2-inch layer of sand will compress about J an inch under the 
above rolling, and consequently the height of the template should 
be adjusted accordingly. To bring the template to the right height, 
^-inch strips should be laid upon the curbs and screeds; and then 
after striking the sand cushion and rolling it, these strips should be 



ART. 2] CONSTRUCTION 509 

removed, and the template be again drawn over the sand to test the 
surface of the sand bed. If the surface is high in spots, the second 
drawing of the template will plane them down; and if there are low 
spots, sand should be sprinkled over them, and the template be 
drawn again. 

The spreading and shaping of the sand cushion is of prime im- 
portance in securing an even surface in the finished pavement; 
and can be successfully done only by careful and skilful men. 

976. At street intersections there are no curbs or gutters to act 
as guides for the template, and hence the above method of striking 
the sand cushion can not be applied. In such cases the sand cushion 
is usually shaped with a hand lute. Stakes about J-inch square 
should be driven at close intervals to aid in bringing the top of the 
sand cushion to the right elevation. 

977. Objections to Sand Cushion. Until comparatively recently 
the only bedding for the brick was a layer of sand about 2 inches 
thick. The purpose of the sand was to level up the foundation and 
to give a good bearing for the brick; and in the early history of 
brick pavements probably a thickness of 2 inches was required for 
this purpose. However, later experience proved that such a great 
thickness was unnecessary and also inadvisable. A better prepara- 
tion of the surface of the concrete foundation, the greater uniformity 
in paving brick, and the closer inspection of the brick made unneces- 
sary so thick a sand cushion. 

There are three serious objections to a sand cushion. 

1. With a thick cushion, it is nearly impossible to secure uniform 
density in the sand layer. The sand is likely to be more moist in 
some spots than in others; and when it dries out, it will shrink and 
leave the brick unsupported, which will ultimately cause a settle- 
ment of the brick and make a depression on the surface of the pave- 
ment. Such depressions are saucer-like, and can be seen in many 
brick pavements. Such depressions are most apparent in pave- 
ments having joints filled with cement grout, since the boundaries 
of the depression are indicated by a break of the bond of the joint 
filler. Tapping the surface of such a pavement, particularly a 
nearly new one, with a hammer will reveal many spots which sound 
hollow, showing that the sand cushion has shrunk away from the 
brick. Such a spot is likely to become a depression. 

2. With a thick sand cushion, the rolling of the pavement is 
almost sure to force the sand up into the bottom of the vertical 
joints between the bricks, and thus prevent the cementitious joint- 



510 BRICK PAVEMENTS [CHAP. XVII 

filler from penetrating the full depth of the brick. Examples are on 
record in which the sand was thus forced nearly or quite to the top 
of the bricks; and not infrequently sand is forced up half the depth 
of the bricks, particularly if the sand of the cushion is fine, as is 
usually the case. 

This objection to the sand cushion is particularly important if a 
rain should wet the cushion before the bricks are rolled ; for if the 
sand cushion is wet, the bricks can not be rolled adequately without 
forcing the sand up into the joints. 

3. Both of the above objections apply to any sand cushion, but 
particularly to a thick one; and the following objection appHes to 
any sand cushion, even a thin one. There is danger that the sand 
cushion may leak away through cracks into sewers, manholes, etc., 
particularly if the wearing course of brick is not water-tight. Such 
flow of sa^id often occurs on steep grades. Cases have been known 
in which a pavement having sand-filled joints and being on a 1 per 
cent grade, sunk next to the curb an inch in twenty years from this 
cause. Even with a water-tight pavement, the sand cushion some- 
times leaks into trenches opened through the pavement and left 
unfilled for a time. A street-railway track has a tendency to cause 
the sand cushion to flow away. The vibration due to passing cars 
has a tendency to break the bond of the joint filling near the rails 
and make a crack that will let water down to the sand cushion, and 
then the water will flow toward the curb and carry the sand with it. 
Further, the track will be forced down by the weight of the car and 
will spring back when the car has passed, thus pumping the water 
in and out, which forces the water through the sand cushion and 
tends to displace it. 

4. Lately some have claimed that the sand cushion served also 
to give elasticity and resiliency to the pavement, and consequently 
protected the brick from excessive wear and possible breakage. It 
is likely that the sand cushion compresses under use, particularly 
if it is not thoroughly compacted before the brick are laid, and also 
if the brick are not firmly settled into the sand cushion by rolHng; 
but under ordinary conditions this compression must be quite small, 
and takes place comparatively soon after the pavement is opened to 
travel, and hence can not have any appreciable effect upon the 
durability of the pavement. Further, little or none of this compres- 
sion is due to the elasticity of the sand cushion, and hence the sand 
cushion can have little or no effect in absorbing shock. The sand 
cushion is a cause of shock rather than an absorber of shock. 



ART. 2] CONSTRUCTION 511 

978. In the early history of brick pavements a 2-inch cushion 
was customary; but later some cities reduced it to IJ inches, some 
to 1 inch, and a few to J inch. At present the better practice does 
away with any mobile sand cushion. 

979. Cement-sand Bedding Course. This form of bedding 
consists of a layer of dry cement and sand about J inch thick. The 
cement and sand are thoroughly mixed dry in the proportion of 
1 : 3 or 1 : 4, and then spread and struck as described for the sand 
cushion (§ 972-74). The mixture of cement and sand, after being 
spread and struck with a template, is so well compacted and of 
such uniform density as not to require rolling; and besides if it is 
rolled, even with a light roller, the bed is so hard as to make it nearly 
impossible to roll the brick to a smooth surface. After the bricks 
for the wearing coat have been set in place upon the mortar bed and 
rolled, the bricks should be thoroughly sprinkled, and care should be 
taken to see that the water really reaches all parts of the sand- 
cement bedding course and converts it into mortar. This can be 
tested by taking up an occasional brick. Subsequently the joints 
in the wearing course are filled with hydrauHc-cement grout, as will 
be described later. 

There are really two types of this form of construction, viz., one 
in which the amount of cement is sufficient to make a mortar of 
fair strength, and another in which the amount of cement is suf- 
ficient only to prevent the cement-sand bed from leaking away or 
shifting under traffic. With the latter form, the bedding course 
was usually 1 or IJ inches, and hence considerable cement was 
required, even though the mixture was a lean one. Gradually the 
bedding course was decreased in thickness and increased in richness. 

980. The cement-sand bedding course has two advantages over 
the sand cushion: 1. It is rigid; and hence can not compress or 
shift under travel, nor leak away. 2. The mortar adheres to the 
foundation and also to the bottom of the brick, and binds them 
together, thus converting the foundation and wearing course into a 
partial monolith. Such a pavement is usually called a semi-mono- 
lithic brick pavement. 

A bed of sand and cement laid as described above never makes 
a really good mortar. In the first place, if the w^ater is applied 
sparingly there is no certainty that enough water reaches the mix- 
ture to make a mortar; and on the other hand, if water is applied 
profusely it may wash the cement out of the sand and destroy the 
mixture as a mortar. Again, even though the mixture receives the 



512 



BRICK PAVEMENTS 



CHAP, xvn 



proper amount of water, the resulting mortar will be of poor quality 
owing to the lack of mixing after the addition of the water. 

981. Apparently the first example of this type of pavement 
was constructed in Baltimore, Md., in 1906; but the most noted 
example is the vehicle entrance to the Pennsylvania Railway 
Passenger Station in New York City constructed in 1910. Another 
innovation in this pavement was that the bricks were only 2J inches 
deep. In 1916, 7,800 vehicles passed over this pavement daily; and 
yet Fig. 178 shows that the surface is still practically perfect. 




Fig. 178. — Semi-monolithic Brick Pavement — Pennsylvania Passenger Station, New 

York City. 



This form of construction was justly popular until the true mono- 
lithic construction was developed, as described in the next section 
below. 

982. Mortar Bedding Course. This consists of a layer of cement 
mortar on which the brick are set while the mortar is still green. The 
chief difference between this form of construction and the cement- 
sand type is that the layer of mortar is placed upon the concrete 
foundation before it has begun to set ; and then the brick are placed, 
rolled, and grouted before the cement in either the concrete base of 
the mortar bed has taken its initial set. With careful work it is 
reasonably certain that the whole construction is really one solid 
mass. This form is known as the monolithic brick pavement. 

There are two slightly different forms of this type of construction. 
In one the concrete foundation is laid in the usual way, and on it a 
IsLver of rather dry cement mortar is spread by means of a template 
similar to that used in gaging the thickness of the sand cushion 



ART. 2] 



CONSTRUCTION 



513 



(§ 972). This form was first used near Paris, 111., in 1914. In 
the other form of construction the concrete foundation is laid about 
half an inch thicker than the depth required, and is then tamped 
with a tamping template (§ 462) to reduce the thickness to that speci- 
fied. The tamping flushes a layer of mortar to the top; and then the 
surface of the concrete, or rather the mortar, is struck off with a 
cutting template, and the brick are set on the mortar surface. This 
form of construction was first used near Danville, 111., in 1915. 

When gravel is used for the coarse aggregate of the concrete 
foundation, the concrete and the mortar bedding course are struck 
off at a single operation with a double template. Fig. 179 shows 
this template. The front template is usually a steel I beam which 




Fig. 179. — Double Template for Striking Mortar Bedding Course. 



strikes the surface of the concrete foundation; and the rear template 
is usually a steel channel, which is | or 3^ of an inch higher than the 
front one, strikes the upper surface of the mortar bedding course. 
The space between the templates is 2 feet wide, and is kept full of 
mortar, which is previously mixed in a small machine mixer. 

Fig. 180, page 514, shows the mortar bed after the bricks have 
been placed upon it and rolled. The mortar is usually forced up 
into the joint | to | of an inch. When a brick is thus removed, the 
surface of the mortar should be damp, but there should be no film of 
water on the top of the mortar. The monolithic type of construc- 
tion has been adopted with great rapidity; but thus far it has been 
employed chiefly on rural roads. 

The monolithic brick pavement is not adapted to a steep grade, 



514 



BEICK PAVEMENTS 



[chap. XVII 



owing to the difficulty of keeping the green concrete at the correct 
grade and cross section. 




Fig. 180. — View of Mortar Bed after Brick Surface had been Rolled. 

983. Comparison of Types. For a comparison of the relative 
merits of brick pavements having the preceding forms of bedding 
course, see § 1023-33. It is not wise to attempt to discuss this 
phase of the subject until the complete construction of the pave- 
ment has been considered. 

984. LAYING THE BRICK. Delivery. The brick are usually 
placed in piles at the side of the road or pavement before the grading 
is done. The brick should be kept clean, and should be handled 
so as not to needlessly nick and break them. 

Formerly there was considerable discussion as to the relative 
merits of (1) delivering the brick along the curb a considerable time 
before they are to be laid, or (2) hauling them to the street as they 
are laid. In the former case, the brick were transported from the 
parking to the men who set them, either in wheelbarrows or by hand 
on a board or later in a pair of tongs. In the latter case, the wagon 
was hauled to the middle of the street on planks, and the bricks were 
carried by hand or with tongs directly from the wagon to the layers. 



ART. 2] CONSTRUCTION 515 

There were some disadvantages in the last method, but there was 
the possibility of saving 2-1 to 3 cents per square yard. 

Both methods have been superseded, as far as street, i. e., wide, 
pavements are concerned, by an improved method of delivering 
brick from the parking to the setters. This device consists of a 
roller conveyor, — a series of rollers set in an inclined frame down 
which the brick roll by their own w^eight in a stream from the parking 
toward the middle of the street, and from which the setters pick 
them to set them into place. This is an example of one of the im- 
provements that have helped to keep the price of street pavements 
down, notwithstanding the advance in cost of materials and labor 
(§637). 

For rural roads, i. e., for narrow pavements, the brick are carried 
by hand on a pallet or in a pair of tongs from the side of the pave- 
ment to the setter. 

985. It is undesirable to use wheelbarrows in transporting the 
bricks from the parking to the setters, since the bricks are likely to 
be chipped in placing them in the wheelbarrow and in dumping 
them out, and further since dumping them is hkely to tilt the bricks 
already set, which will make the surface of the finished pavement 
uneven and rough. 

986. If the brick are delivered to the setters in tongs or on a 
pallet, the men should be provided with planks to walk upon ; and 
they should not be allowed to step upon the bricks before they are 
rolled, as it is liable to tilt them and cause the surface of the pave- 
ment to be rough after it is rolled. Further, workmen should not 
be permitted to track mud upon the brick. When the condition of 
the ground is such that mud will be tracked upon the pavement, the 
work of laying brick should not be allowed. 

987. Direction of Courses. It is customary to lay the brick 
with the length perpendicular to the curb, except at street inter- 
sections; but there are a few cities in which the brick are laid in 
courses making an angle of 45° with the length of the street, with 
the idea that the tendency to form ruts would be less if the wheels 
crossed the bricks diagonally. There is no advantage in the diagonal 
over the square courses; they are more difficult to lay, cutting the 
corner of the brick in making the fit next to the curb is wasteful of 
material, and the diagonal courses do not give as good foothold to 
the horses. 

The hill-side brick shown in Fig. 170 and 171, page 483, must be 
laid with its length in the direction of the street. 



516 



BRtCK PAViEMENTS 



[chap, xvii 



Occasionally a few courses of brick are laid longitudinally in the 
gutter, similar to the practice with stone blocks; but this is unneces- 
sary, since the brick pavement is much smoother than the ordinary 
stone-block pavement, and besides the running joint where the trans- 
verse and the longitudinal sections join is likely to develop into a rut. 

988. At street intersections and junctions the bricks should be 
laid diagonally — a compromise position between the directions of 
the travel on the two streets. Street intersections need special care 
in construction, since they are exposed to the traffic of two streets. 
Fig. 181 shows the usual arrangement of the courses for a street 




Fig. 181. — Double-diagonal Brick Intersection. 



intersection; and Fig. 182 and Fig. 183 (page 518) show two other 
arrangements that have occasionally been used. Slight objections 
have been urged against all three plans. The bond in Fig. 181 is 
weak along the middle Une of each street; Fig. 182 is objectionable 
owing to the tendency of ruts to form along the lines running through 
the ends of the bricks; and Fig. 183 is defective since traffic around 
the corners A and B is parallel to the courses of brick. 



ART. 2] 



CONSTRUCTION 



517 



At a street junction only half of the common area should be laid 
with diagonal courses. For example, assuming that in Fig. 181 
the street enters the lower side of the transverse street but does not 
cross it, then the lower half of the intersection would be laid with 
courses as in the diagram, while in the upper half the length of the 
bricks would be perpendicular to the transverse street. 

989. Setting the Brick. In setting the brick the m.an should 
stand on those already laid, and not upon the sand cushion. Under 
no consideration should the sand bed be disturbed. The brick should 
be set on edge as closely and compactly as possible, each being 



' I . ' I ' I . I I . I 1 . 1 . 1. 1 . ' ' ' -T 



I ' I I I I I I I I I 




Fig. 182. — Herring-bone Brick Intersection. 



pressed or rather bumped both endwise and sidewise against those 
already laid. The bricks are stronger and more durable than any 
material that can be used to fill the joints, and consequently the 
thinner the joints the better. The bond should be approximately a 
half brick. If the brick were laid without bond, ruts would form 
along the continuous end-joints; and therefore the more the bond 
the better. No bats should be used, except in making closures; and 



518 



BRICK PAVEMENTS 



[chap. XVII 



in cutting a brick to close a course, care should be taken to get a 
square end and to make as tight a fit as practicable. As far as pos- 
sible, the bats should be obtained from chipped and broken brick, 
or from misshapen ones rejected in the inspection after the brick 
are set. It is usually specified that no bat less than 2J inches long 
shall be used. Under this specification, if the space is less than 2i 
inches, it is necessary to take up the next brick and chip enough off 
to permit the use of a bat more than 2^ inches. Fig. 184 shows the 
hammer employed in cutting, or rather in breaking, a brick to close 
a course. 




Fig. 183. — Single-diagonal Brick Intersection. 



In some cities it is required that each four or five courses of brick 
shall be driven up from the face by striking with a sledge against a 
1" X 4" or 4'' X ^' timber resting against the last course; but this 
is unnecessary, if each brick when laid is pressed, or rather bumped, 
against the side of the course already in position. In any case the 
courses should be straight across the street; and if they are not laid 
so, they should be straightened by driving up each four or five 
courses from the face. Sometimes the bricks in a row are crowded 




ART. 2] CONSTRUCTION 519 

together endwise by inserting a crowbar at the curb; but this is 
unnecessary, provided each brick as it is laid is bumped against 
the end of the preceding one. 

It is usually specified that nothing smaller than a 2j-inch bat 
shall be used in making a closure. The alternative is either to close 
up the joints between the ends of the 
bricks by prying with a crowbar until a 
larger bat can be inserted, or to open up 
a few joints until the space at the end of 
the course is moderately small. The latter 
is undesirable, since it is likely to displace 
the brick vertically so as to make the 
surface of the pavement rough after it 
has been rolled. 

Of course, lug brick should be set with Fig. 184.— Brick Paver's 

the lugs always in the same direction. 

990. Inspecting. After the bricks are laid, the pavement should 
be inspected, all soft, broken, and badly misshaped brick being 
marked for removal. To reveal the soft brick, it is customary to 
sprinkle the pavement heavily with a hose. While the w^ater is 
being applied, the soft brick will appear comparatively dry; but after 
the sprinkling is stopped, the soft brick will appear to be the wetter. 
A brick having only a small piece chipped from the corner or edge 
may be turned over. Objectionable brick may be marked with 
chalk, a cross or circle indicating a brick to be removed and a single 
straight line one to be turned. Rejected brick are removed with 
tongs having broad flat noses and long stout handles. 

991. Rolling. After all rejected brick have been removed and 
the pavement has been swept, it is ready for rolling. The purpose 
of the rolling is to settle the bricks uniformly into the bedding course. 
A heavy roller is undesirable, at least in the beginning of the rolling, 
since the first passage of it tilts the bricks to one side so much that it 
is nearly impossible to straighten them up again. Unless the top 
faces of the bricks are brought to a plane, the pavement will be rough 
and noisy, and will lack durability. 

It is important that the rolling shall closely follow the spreading 
of the bedding course, so that a shower may not wet it. Whatever 
the material of the bedding course, if it is rained upon, the bricks 
with unfilled joints should be taken up and a new bedding course be 
spread. For much the same reason the filling of the joints (§ 994- 
1005) should closely follow the rolling. 



520 



BRICK PAVEMENTS 



CHAP. XVII 



If the bedding course is sand or dry sand suk^ cement, the roller 
should weigh 3 to 5 tons; but if the bedding course is green mortar 
(§ 982), the rolling should be done with a hand roller about 30 inches 
in diameter, 24 inches long and weighing from 600 to 900 lb. The 
rolling should be continued until the surface of the pavement is 
smooth. 

The pavement should first be rolled longitudinally, beginning 
at the crown and working toward the gutter, taking care that each 
return trip of the roller covers exactly the same area as the preceding 
trip so that the second passage of the roller may neutralize any 
careening of the brick due to the first passage. Pavements that 
have been rolled only once or always in one direction, are very much 
rougher and more noisy than when properly rolled. If a spot is 
skipped on the return passage of the roller, it can be detected by a 
casual inspection or by the noise of a passing vehicle. The first 
passage of the roller should be made at a slow speed to prevent undue 
canting of the brick. After the pavement has been rolled longi- 
tudinally, it should be rolled back and forth transversely, or at least 
in both directions at an angle of 45° from curb to curb. If the 
pavement is narrow, and particularly if it has a high crown, it may 
not be wise to roll it transversely or even diagonally, because of the 

time required and also because of the probability of 

breaking brick. In this case the longitudinal rolhng 

should be more thorough. 

If the rolhng is well done, the sand cushion will 

be pushed up between the brick | to f of an inch. 

992. There are sometimes places which can not 
be reached by the roller, for example around manhole 
covers; and in these cases the brick should be settled 
to place by ramming. The ramming should be done 
with a paver's rammer, Fig. 185, wighing not less 
than 50 lb. The ramming should be done on a 2-inch 
plank 10 to 12 inches wide and 6 feet long laid parallel 
to the curb. The ramming should be continued until 
the pavement has a good surface at the proper ele- 
vation. 

993. After the rolling is completed, the joints 
Fig. 185.— Paver's g^Q^ifj \)q inspected; and if the bedding course has 

Rammer. '■ i i • i i i 

been forced up between the bricks more than f an 
inch, the bricks should be taken up and relaid. 

It is usually specified that after the final rolhng the surface of 




ART. 2] 



CONSTRUCTION 



521 



the pavement shall be tested with a 10-foot straight edge laid 
parallel to the length of the street, and any depression exceeding 
i of an inch shall be taken up and re-laid. 

Fig. 186 shows a monohthic brick pavement after it has been 
rolled and before the apphcation of the filler. The two-section 
hand roller used in rolhng the bricks stands in the foreground. 




Fig. 186. — Monolithic Brick Pavement Rolled and Ready for the Filler. 

994. JOINT Filler. The joints should be filled (1) to keep the 
brick in the proper position, (2) to lessen the chipping of the edges of 
the brick, and (3) to prevent water from penetrating to the cushion 
coat and to the foundation. Three forms of filler are in common 
use, viz.: sand, hydraulic-cement grout, and bituminous cement, 
i. e., asphalt or tar; and recently a mixture of tar and sand has been 
used. 

995. Sand Filler. Sand was the first filler employed for brick 
pavements, and in the Middle West is even yet largely used. The 
sand should be fine and dry, and be worked into the joints by sweep- 
ing it over the pavement, which also should be dry. Although the 
sand is nominally swept into the joints, it is usually simply spread 
upon the surface and left to be worked in by travel, which is unde- 
sirable since the joints are then partially filled with manure and 
street dirt. The sand can be swept into the joints effectively and 
economically with a revolving machine sweeper. After the joints 



522 ■ BRICK PAVEMENTS [cHAP. XVII 

have been filled, the surface of the pavement is covered with a layer 
of sand i to J inch thick, which is left on for a few weeks after the 
street is thrown open to travel, to secure the thorough working of the 
sand into every joint. 

The cost of sweeping the pavement and filling the joints with sand 
is 0.2 to 0.3 cent per square yard, and the cost of a J-inch layer of 
sand at SI. 08 per cubic yard is 1.5 cents per square yard. To cover 
waste and contingencies, the sand joint-filler is usually estimated at 
2 cents per square yard. 

The advantages of a sand filler are: 1. It is cheap. 2. The 
pavement may be thrown open to traffic as soon as the bricks are 
laid. 3. The pavement may be taken up easily and without break- 
age of the brick. 4. It is practically water tight, particularly 
after being in service a short time. Whenever a brick pavement 
having a sand filler is opened, the sides of the brick are always found 
dry and clean a Httle distance below the wearing surface. 

The disadvantages of a sand filler are: 1. It does not protect the 
edges of the brick from chipping. 2. It may wash out from the crown 
toward the gutter. 3. It is removed from the top of the joints by the 
street sweeper — either the broom or the pneumatic, — and by auto- 
mobiles. 

996. Cement Grout. The grout should be composed of part 
Portland cement and 1 or IJ parts sand. If the sand is well graded, 
1 part of cement wiU fiU the voids of IJ parts of sand, and give a 
filler of maximum strength; but if the sand is not well graded, the 
grout should be 1 : 1. The cement should meet the requirements of 
the standard specifications. The sand should not contain more than 
1 per cent by weight of clay or loam, and should contain such gra- 
dation of sizes that all will pass a 20 standard sieve and all be re- 
tained on a 100 standard sieve. Some contractors place the sand in 
bags when unloading it from the car, and distribute the bags of sand 
with an equal number of bags of cement at proper intervals along 
the pavement, which secures the proper proportion of ingredients 
and prevents loss of materials and time in measuring. The sand 
and cement should be mixed dry until the mass is homogeneous and 
of a uniform color. The cement and sand should be mixed dry so 
that the cement will not ball up when the water is added. For the 
best results a considerable amount of this mixture should be pre- 
pared at one time, but not more than will be used up in two hours. 

To prepare the grout, a small batch of the mixed sand and cement, 
preferably not more than 2 cubic feet, should be placed in a suitable 



ART. 2] 



CONSTRUCTION 



523 



box or machine, and water should be added to make a grout that will 
freely flow to the bottom of the joints without separation. It is 
important that the water be added slowly and that the grout be 
mixed thoroughly. For the best results, the dry mortar should first 
be reduced to a uniform and plastic mortar, and then more water 
should be added, while the mass is mixed vigorously, until the desired 
consistency is attained. 

997. Mixing Box. The mixing may be done in a box made for 
the purpose, which should be 3J to 4 feet long, 27 to 30 inches wide, 
and 14 inches deep, and should have legs of different lengths, so that 
the mixture will readily flow to one corner of the box, which should 
be 8 to 10 inches above the pavement.* 

The grout should be removed from the box to the pavement 
with a scoop shovel, and not by overturning the box upon the pave- 
ment; since by the last process the sand, cement, and water are 
separated, and are deposited in different portions of the pavement. 
While the box is being emptied, the grout should be constantly 
stirred to prevent a separation of the sand from the cement. 

A mortar box should be provided for each 10 or 12 feet of width 
of pavement. 

998. Mixing Machine. Recently a small mechanical mixer 




Fig. 187. — -Grout-mixing Machine. 



been introduced for preparing the grout. Fig. 187 and 188 
show such a machine. In using the machine, it is important that 



* The National Paving Brick Manufacturers Association publish complete specifications 
and working drawings for such a box, which may be had gratuitously of the Secretary, Cleve- 
land, Ohio, 



524 



BRICK PAVEMENTS 



[chap. XVII 



the mixing be not hurried; and that the conditions stated in the 
second paragraph of § 996 be observed. 

Some engineers permit the use of the machine for mixing the first 
apphcation of grout, but not for the second, as the latter should be 
stiffer. However, if carefully manipulated, the machix^e will make 
as good grout as can be made in a box; and besides the mixing is less 
likely to be slighted, and the cost of mixing is less. 




Fig. 188. — Grout-mixing Machine at Work. 



999. Applying the Grout. Before the grout is applied to the 
pavement, the brick should be thoroughly wetted by being gently 
sprayed. A strong stream is likely to displace the mortar. The 
grout should be applied to the pavement in small quantities, and 
should be quickly swept into the joints with an ordinary brush broom. 
The strokes of the broom should be mostly lengthwise of the brick 
to most effectively get the grout into the joints. It is better that 
the joints should be only about half or two thirds filled at the first 
application, since then there is a less depth of grout in the joints and 
consequently less hability of the separation of the sand, the cement, 
and the water. 

Fig. 189 shows the process of making the first application of 
cement-grout filler using mixing boxes. Notice that the filler is 
dipped out of the box and poured upon the pavement with scoop 
shovel; and that the grout is spread with brush brooms. 

In applying the cement filler it is very important that the grout 
shall not bridge across or dam up a joint; and care should be taken 
to see that the grout really reaches the bottom of all joints. 



ART. 2] 



CONSTRUCTION 



525 



1000. If a grout filler is to be used with a sand cushion, the first 
application of filler should be made very thin, so that it will pene- 
trate the sand that is pushed up into the joint by the rolling and 
convert the sand into mortar. If the sand in the bottom of the joint 
is not thus converted into mortar, the bricks are likely to spall on the 
top owing to concentrated pressure at the top of the joint, due to the 
expansion of the pavement. 

In making this very thin grout, it is necessary first to mix the sand 
and cement dry, and then to add water gradually and stir the mix- 
ture vigorously, until a good stiff mortar is produced, and next to 




Fig. 189. — First Application op Grout Filler. 



continue the gradual addition of water and the mixing until a very 
thin mortar results. If all the water is added at once, or if the 
water is added too rapidly, or the mortar is not thoroughly and con- 
tinuously mixed while the water is being added, it is nearly impos- 
sible to keep the sand, cement and water from segregating. 

1001. After the first application has been carried forward 40 or 
50 feet, and after it has settled but before the initial set has begun, 
a second appUcation should be made in the same manner as the first, 
except that the grout should be somewhat thicker. 
'^ Fig. 190 shows the process of making the second application of 
grout filler, when the mixing bases are used. The grout is dipped 



526 BRICK PAVEMENTS [CHAP. XVII 



with a scoop shovel and spread with a squeegee, a wooden scraper 
having a rubber edge. 

1002. After the second appHcation has settled but before initial 
set has begun, all surplus grout on the surface should be forced along 




Fig. 190. — Second Application of Grout Filler. 

over the pavement with a squeegee. The squeegee should always 
move at an angle with the joints, thus leaving them level full. 

In making the final finish, the squeegee should be drawn, not 
pushed, over the surface; or in other words, the workmen should not 
track up the finished surface, for doing so raises httle projections on 
the surface of the grout which when hardened are very destructive 
upon automobile tires. This precaution was not observed in building 
the automobile brick race-track at Indianapolis, even though rec- 
ommended by the engineer; but after the track was completed, it was 
necessary to spend considerable time and money to remove these pro- 
jections. Of course, on a pubHc highway these projections will 
ultimately be worn off by steel-tired vehicles; but in the meantime 
much damage will be done to auto tires, and it costs practically noth- 
ing to prevent the projections. 

Fig. 191 shows a vertical view of a perfectly grouted brick pave- 
ment. Fig. 192 shows a well-grouted Ohio rural brick road. 

Fig. 193 shows a sand-cushion cement-grouted brick pavement 
on South Sixth Street, Terre Haute, Indiana, when 28 years old. 
This is one of the first, if not the first, cement-grouted brick pave- 



ART. 2] 



CONSTRUCTION 



527 



ment; and it is in a remarkably good condition. The view was 
taken two blocks from the main business street. When this pave- 



FiG. 191. — Vektical View of a Pekfectly Grouted Brick Pavement. 

ment was laid Terre Haute had a population of 30,217^ and in 1910 
it had 58,157. The joint filler and the brick have worn down to- 
gether, and the surface is as smooth as a marble mosaic. The top 




Fig. 192. — A Well-grouted Ohio Rural Road. 



faces of the brick are flat, and the joints are level full of cement grout. 
Scarcely a single chipped or broken brick can be found; and the 



528 



BRICK PAVEMENTS 



[chap. XVII 



general wear, in the middle third of the street, has been only about yj 
to re of ^^ i^ich of depth, with a very few holes i inch deep caused 
by soft brick. The brick are not as good as those made at the present 
time; but the pavement, particularly for that time, was unusually 
well constructed. It was provided with an adequate foundation, 




Fig. 193. — Sand-cttshion Cement-gkouted Brick Pavement 28 Years Old. 



the brick were well burned, and were carefully and thoroughly rolled, 
and the joints were entirely filled with good portland-cement grout, 
and consequently this pavement has worn exceedingly well. Of 
course other pavements constructed with as good material and with 
the same care would wear equally well. 

1003. With hill-side brick (§ 936) the grout should be swept from 
the grooves before it sets. 

1004. After the joints have thus been filled, and after the grout 
has set so that a coating of sand or earth will not absorb moisture 
from the joint filler, a half inch of fine sand should be spread over the 
entire surface of the pavement; and if the weather is very hot or 
dry, the sand should be sprinkled at intervals for two or three days, 
to insure that the cement does not lose by vaporization the water 
necessary for chemical combination in setting. Some engineers 
prefer hay or straw instead of sand or loam, since they can be moved 
ahead and used a second time. 

Travel should be kept off the pavement from seven to ten days, 
or at least until the cement has fully set, and it is much better if 



AiRT. 2] CONSTRUCTtON 529 

travel is kept off longer. Some engineers specify three weeks in 
warm weather, and longer for cold weather. If the cement filler is 
disturbed before it is firmly set, it is practically no better than sand. 
If the cement filler is put in as described above and allowed to set 
firmly before travel is admitted, the filler will wear no faster than the 
best paving blocks and will prevent spalling and chipping of the 
bricks at the edges and corners. 

1005. To separate the grouted section from the ungrouted por- 
tion, a row of metal strips A by 6 by 36 inches should be inserted in 
a transverse joint of the pavement. By this means the grouting will 
end in a transverse joint. These metal strips should be removed 
when the grout has become stiff, but before initial set. 

1006. Cost. The amount of grout required will vary with the 
openness of the joints, and also with the quantity of sand of the 
cushion course that works up into the lower part of the joints while 
the bricks are being rolled. 

'' If a 1 : 1 portland-cement grout is used, the area filled with 
one barrel of cement will be as follows : With 4-inch brick and a sand 
cushion, 32 square yards of re-pressed brick, and 24 square yards 
of wire-cut lug brick; and with 4-inch brick on a |-inch mortar bed, 
30 square yards of re-pressed brick, and 22 square yards of wire-cut 
lug brick."* It is quite common to estimate f of a barrel of cement 
per square yard for 1 : 1 grout. Of course, the cost of the cement 
for the filler will vary with the market price of cement. The grout 
will require about 0.2 cubic foot of sand per square yard of pavement; 
and its cost at $1.00 per cubic yard, will be about 0.7 cent per square 
yard of pavement. The cost of applying the grout filter will 
vary considerably with the details of doing the work, i. e., the number 
of apphcations, and whether the mixing is done in a box or a machine; 
but the cost will usually be 2 or 3 cents per square yard. The total 
cost of grout filler was formerly 8 to 10 cents per square yard, but in 
1917 was usually 10 to 12 cents per square yard. 

1007. Merits. The advantage of the cement filler is that it pro- 
tects the edges of the bricks from chipping, and thus adds to the 
durability of the pavement. When the joints are filled with sand, 
the edges of the brick chip off, the upper faces wear round, the pave- 
ment becomes rough, and the impact of the wheels in jolting over the 
surface tends to destroy the brick; while with a good cement filler, 
the edges do not chip, the whole surface of the pavement is a smooth 

* H. E. Bilger, Road Engineer, Illinois Highway Commission, in Engineering and Contract- 
ing, Yol ^6 {1916), p. 502. _ .^ 



530 BRICK PAVEMENTS [CHAP. XVII 

mosaic over which the wheels roll without jolt or jar, and conse- 
quently the life of the pavement is materially increased. Fig. 193, 
page 528, shows a grout-filled pavement 28 years old upon which there 
have been practically no repairs. See the last paragraph of § 1002 
for a description of its present condition. 

An objection to the cement filler is that it does not take up the 
expansion of the pavement due to increase of temperature, and that 
consequently the pavement is likely to rise from the foundation and 
give out a rumbling noise as vehicles go over it. This rumbling 
can be ehminated by inserting longitudinal expansion joints as 
described in § 1017. 

Another objection to the cement filler is that in making repairs 
it is difficult to remove the bricks without breaking many, and it is 
difficult to clean the bricks so that they may be used again. This 
is an advantage, if it will in any degree prevent the tearing up of the 
pavement; and at best this objection ought not to have much weight 
against durable construction. 

A third objection is that the street can not be used while the 
cement is setting. Often the cement is not allowed to set fully 
before throwing the street open to travel, and consequently the chief 
advantage of the rigid filler is lost. The semi-monohthic and the 
monolithic types of construction are free from this objection (§ 979 
and §982). 

1008. Bituminous Filler. Both asphalt and tar are used as a 
filler for the joints of a brick pavement. 

1009. Asphalt Filler. The various producers and refiners of 
asphalt prepare a grade of asphalt particularly for use as a filler for 
brick, stone-block, and wood-block pavements. For the specifica- 
tions of such, see § 544. 

1010. Tar Filler. For the specifications of a tar suitable for a 
joint filler for brick pavements, see § 576-77. 

1011. Applying Bituminous Filler. The bricks should be dry, 
and the bituminous filler should be hot enough to flow freely and 
adhere to the brick. The asphalt fillers should be appHed at a tem- 
perature of 350 to 450° F., and the tar fillers between 300 and 350° 
F. If either filler must be heated hotter than this to make it pour 
freely, then it will be so hard as to chip out of the joint in cold weather; 
and if it can be poured much colder than this, it will be so soft as to 
run out of the joints in hot weather. However, manufacturers vary 
the temperature of pouring to fit extreme cHmates. 

The bituminous filler is poured into the joints through the point 



A.RT. 2] CONSTRUCTION 53l 

of a cone-shaped pouring can. The point of the can has a cast iron 
tip with an opening in it about J inch in diameter. The tip is opened 
and closed by a valve, which is operated by a handle projecting at the 
top of the can. The cast iron tip is placed in a joint, the valve is 
opened, and the can is drawn along as the joint becomes filled. A 
helper fills the can as it is emptied. 

As soon as the joints in a short section of the pavement have 
been filled, and while the bituminous cement is still soft, a light 
layer of sand should be spread over the pavement, but only enough 
to prevent the cement from sticking to passing wheels. In cold 
weather the sand should be heated so as to bond readily with the 
pitch. 

Particular care should be taken in applying the filler around man- 
holes, at the gutter, etc., to prevent leakage of water into the sub- 
grade. 

1012. A pouring can, or rather tank, having multiple spouts 
has recently been put upon the market. The tank is mounted upon 
wheels, and somewhat flexible spouts project below. The tips of 
the spouts are placed in the joints, and the tank is drawn along by 
hand as the joints are filled. 

Contractors claim that it is materially more difficult to fill the 
joints of a pavement made of wire-cut lugs than of re-pressed brick, 
as with the former it is more difficult to keep the tip of the pouring 
can in the joint. Recently bituminous filler has been successfully 
applied with a squeegee. The only objection to this method is that 
the cement may be chilled by contact with the brick and fail to 
penetrate to the full depth of the joint. 

1013. Cost The cost depends upon the locality, the closeness 
of the joints, and the amount of bituminous material left upon the 
surface of the pavement. A tar filler usually costs 8 to 10 cents per 
gallon and asphalt about 10 to 12; and 1 to IJ gallons is generally 
required for a square yard of pavement. The labor of heating and 
pouring is usually about 5 to 7 cents per square yard. The total 
cost of a tar filler is therefore about 13 to 15 cents per square yard, 
and of asphalt about 15 to 19 cents. 

1014. Merits and Defects. A bituminous filler is superior to 
sand in that it makes a perfectly water-tight pavement, and better 
protects the edges of the bricks. Bituminous filler is preferable 
to cement grout in that the pavement can be opened to travel as 
soon as it is laid; but bituminous filler does not protect the edges of 
the brick as well as grout. 



532 



BRICK PAVEMENTS 



[chap. XVII 



1015. Tar-sand Filler. Recently a mixture of tar and sand, 
usually called tar mastic or pitch mastic, has been employed as a 
joint filler for brick pavements. The tar pitch should conform to the 
specifications in § 576-77. The filler is made of pitch and as much 
fine clean sand as the pitch tar will carry, usually about 1:1; but 
in no case should the volume of the sand exceed that of the tar. 
The coarser the sand, the smaller the proportion of it should be used. 
The sand when mixed with the tar should be at a temperature be- 
tween 300° and 400° F. ; and the tar shall be heated to 250° to 325°. 
The mixing is most easily done with a hoe in a wheelbarrow or a 
concrete buggy. The mastic is poured on the pavement and pushed 
into the joints with a squeegee. 

Fig. 194 shows the method of applying tar-mastic filler. The 
smoke indicates that the sand was too hot. 

This filler has been used for brick pavements in a few cases with 
every evidence of success; but the experience is too Hmited in both 




Fig. 194. — Applying Tar-sand Filler. 



extent and time to establish the merits of the method. A tar-sand 
filler protects the edges of the bricks better and is less susceptible 
to temperature changes than tar alone; and the only question is 



ART. 2] CONSTRUCTION 533 

whether or not the tar-sand filler can be made so as to flow satis- 
factorily into the joints of a brick pavement. Since the joints of 
stone-block pavements (Chapter XVIII) are wider than those of 
brick pavements, such a filler is more needed and can be more sat- 
isfactorily applied to the former than to the latter. For specifica- 
tions for a tar-sand filler, and for further details concerning its use, 
see § 110. 

1016. Expansion Joints. Expansion joints may be either 
longitudinal or transverse. 

1017. Longitudinal Joints. With a sand filler (§ 995) there is 
little or no need for expansion joints, since the sand in the joints 
will yield enough to compensate for the expansion or contraction 
due to changes of temperature. For much the same reason, expan- 
sion joints are not necessary with a bituminous filler (§ 1008). But 
with a rigid grout filler and sand bedding-course, it is necessary to 
construct longitudinal expansion joints next to the curb or gutter on 
each side, to provide for the expansion and contraction due to changes 
of temperature in the wearing course. To be perfectly safe the 
expansion joint should extend to the bottom of the concrete base; 
although often it reaches only to the top of the concrete base. The 
omission of longitudinal expansion joints is Kkely to cause the ex- 
pansion of the wearing course to Hft the brick from the bedding 
course and to cause the pavement to give out a deafening noise 
when a heavy-laden steel-tired vehicle goes over it at any consid- 
erable speed ( § 1027) . 

The longitudinal expansion joint may be made by placing a 
J- to 1-inch board on edge against the curbs; and then after the 
bricks are set withdraw the plank and fill the space with tar or 
asphalt. A close examination of Fig. 171, page 483, will show such 
a plank in position wdth wedges between it and the curb to facilitate 
the removal of the board. An objection to the poured expansion 
joint is that it is liable to get blocked by a pebble or a brick spaU 
getting into the space before the bituminous material is poured. 
Instead of using the plank as described above, a much better way is 
to place pre-moulded strips of mastic next to the curbs before laying 
the brick. There are several forms of these strips on the market. 
The strips are usually f of an inch thick for a pavement 20 to 30 
feet wide, and proportionally thicker for wider pavements. The 
strips are comparatively short, and should fit closely end to end; 
and should extend the full depth of the brick, and should be stiff 
enough to stand alone in place until the bricks are placed against 



534 BRICK PAVEMENTS [CHAP. XVII 

them. The material should be pliable at 32° F., and should not 
melt or flow at 125° F. 

A true monohthic pavement needs no longitudinal expansion 
joints, although they are sometimes provided. 

1018. Transverse Joints. Transverse expansion joints are not 
needed with either a sand or a bituminous filler. Opinions differ 
as to the need of such joints with grout filler; but the best practice 
seems to be to omit them. 

There are two forms of transverse expansion joints in use. In 
one method two or three or four of the transverse joints between the 
courses of brick are filled with bituminous cement. In the other 
method a J-inch plank is inserted between courses of brick at inter- 
vals of 25 to 50 feet; and then after the brick are laid and grouted, 
the plank is removed and the space is filled with bituminous cement. 
.Or, instead of the plank, a pre-moulded sheet of mastic (§1017) is 
used. 

1019. There are several objections to transverse contraction 
joints in a pavement having a grout filler. 

1. The expansion joint is weaker than other joints, and hence 
the weight of passing wheels is likely to break the bond of a brick 
next to the joint, and then the bond of one brick after another fails 
in succession. 

2. The contraction joint concentrates all of the shortening of a 
section of the pavement at one line, and opens the contraction joint 
so as to permit water to enter the sand cushion. The water acts as 
a lubricant and causes the sand to shift, and often permits a brick 
to settle; and then the impact of a passing wheel breaks the bond of 
another brick, and the defect gradually extends. The water may 
freeze and lift the pavement, which rarely returns to its former 
position, for the same reason that the continued action of frost lifts 
loose stones to the top of the ground. If there are no contraction 
joints, the contraction is likely to open many narrow cracks which 
are less harmful than a few wider ones. 

3. The filler in the expansion joint becomes more rigid at the 
top than at the bottom, partly by vaporization and oxidation, and 
partly by the pounding in of street dirt; and consequently the 
expansion of the pavement concentrates pressure at the top of the 
joint, and the adjoining brick are spalled. This roughens the pave- 
ment and increases the effect of impact, which breaks the bond and 
causes the sand cushion to shift. If there are no transverse expan- 
sion joints, the expansion simply produces compression in the pave- 



ART. 2] 



CONSTRUCTION 



535 



merit and does no harm. This conclusion is in harmony with expe- 
rience with concrete pavements (§466-68), namely, that trans- 
verse expansion joints are not only not needed, but are a positive 
detriment. 

1020. Fig. 195 shows two examples of failures due primarily to 
a contraction joint. In the left-hand view the wheel-track crosses 
the joint near the middle of the picture; and doubtless the damage 




Fig. 195. — Failuees at Transverse ContractionLJoints, 



started at this point and gradually progressed in all directions, for 
each of the three reasons explained in § 1019. In the right-hand 
view the contraction joint slopes up and to the right across the 
picture. For some reason the damage is more to the right of the 
joint than to the left, perhaps because of defective grouting (§ 1059). 

1021. Expansion Joints at Anchors. An expansion joint J to 
f of an inch wide should be provided around manhole covers, water 
boxes, etc., which might act as anchors to prevent the expansion of 
the pavement. Frequent examples are seen where the pavement 
buckles at such points owing to the lack of adequate provision for 
expansion. 

1022. Headers. A header is a wood or stone or concrete curb 
or protection placed at the end of the pavement or at an alley and 
street intersection, to protect the edge of the pavement from vehicle 
wheels bumping against it in getting on the pavement. A w^ood 
plank 2 to 4 inches thick, held in position by posts, is sometimes 
used; but stone or concrete are more durable, and are not much 
higher in first cost. A 4-inch hard limestone or a 6-inch concrete 
slab is usual. 



536 BRICK PAVEMENTS [CHAP. XVII 

With a monolithic brick pavement the header is not absolutely 
necessary, as the brick will stand a good deal of bumping without 
being dislodged; but even in this case the use of a substantial header 
is true economy. 

1023. COMPARISON OF TYPES OF BRICK PAVEMENTS. Brick 
pavements differ chiefly as to the nature of the bedding course and 
the character of the joint filler. The different types will be com- 
pared as to durabihty, smoothness, noisiness, thickness, time in 
construction, and cost. 

1024. Durability. The durabihty depends chiefly upon the ma- 
terial of the joint filler. The merits of the several joint fillers have 
already been considered; and hence little need be said here. How- 
ever, it may be repeated that a cement-grout filler protects the 
edges of the brick best, and that such a filler makes the most durable 
pavement. 

1025. Smoothness. It has been abundantly proved by expe- 
rience in the field that it is easier to get a smooth surface with a 
mortar bedding-course than with a sand cushion. Smoothness 
promotes durabihty; and besides the smoother the pavenient the 
less noisy it is. 

1026. A grout or a bituminous filler is not retained in the joints 
of re-pressed brick as well as of those not re-pressed, since the former 
have a rounded edge while the latter have a square edge. With a 
rounded edge, if the joint is filled level full, the filler feathers out at 
its edges and is easily crumbled off; and then the next wheel drops 
into the depression, and breaks out more of the filler. Soon the 
filler is broken out to a considerable depth, and then the joint be- 
comes a groove into which each passing wheel drops with a bump that 
disintegrates the edge of the brick. With a square-edged brick the 
joint filler wears away only as fast as the face of the brick. 

1027. Noisiness. A brick pavement may produce noise from 
two causes. One of these is the roughness of the surface, w^hich has 
just been considered in the preceding paragraph. 

The second occurs only with a sand bedding-course and grout- 
filled joints, and is due to the fact that the wearing course is sepa- 
rated from the bedding course, which causes the pavement to give 
out a rumbhng or roar when a steel-tired wheel goes over it. This 
separation may be due to the drying out of the sand cushion in spots, 
which causes it to shrink away from the brick wearing coat. Many 
brick pavements rumble from this cause. When this occurs the 
pavement gives out a rumbling when a steel-tired wheel goes over 



ART. 2] CONSTRUCTION 537 

one of these hollow spots. Sometimes a high temperature lifts the 
whole w^earing coat up from the bedding course, when the noise is 
very marked. Something like the same result occurs in cold weather, 
possibly owing to the expansive action of freezing water in the soil 
behind the curb crowding the curbs inward and thus hfting the 
wearing coat up from the bedding course. If each curb of a 40-foot 
pavement is forced inward -^ of an inch, the crown of the pavement 
will be lifted from the foundation more than an inch. This result 
will occur only when the subsoil outside of the curbs freezes while it 
is at least nearly saturated with water. 

Both the semi-monolithic and the monolithic types of brick pave- 
ment are free from any rumbling noise. 

1028. Thickness. Nominally there are three forms of bedding 
courses; but really there are only two, viz.: sand, and cement 
mortar. A brick pavement has thickness primarily to enable it 
to distribute the concentrated load of a wheel over sufficient area 
of the subgrade to enable the native soil to support the load. The 
pavement distributes the load mainly, if not wholly, by its strength 
as a beam, which enables it to bridge over any soft spot and also to 
resist the hfting action of frost in the subgrade. 

The thickness of a brick pavement having a sand cushion is 
about as follows: foundation, 6 inches; sand cushion, 2 inches; 
and wearing coat, 4 inches, — a total of 12 inches; but considered 
as a beam, the effective thickness of such a pavement is only that 
of the concrete base, i. e., 6 inches. The thickness of a pavement 
having a cement mortar bedding-course. is as follows: foundation, 
6 inches; bedding course, 1 inch, and wearing coat, 4 inches, — a total 
of 11 inches; but considered as a beam, the effective thickness of such 
a pavement is 11 inches. The strength of a beam varies as the square 
of its depth, and therefore the relative beam strength of the two 
pavements as above is as 36 to 121; or the monolithic pavement 
considered as a beam is 3.35 times the stronger.* Even though 
there may not be a perfect union between the foundation and the 
wearing coat, the above ratio is nearly correct, for the bedding 
course is nearly at the center of the beam and hence there is little 
or no longitudinal shear upon it, and hence the pavement acts nearly 
as a solid beam. Laboratory experiments show that a well-grouted 
layer of brick has as great transverse strength as a concrete slab 
of equal depth. 

* For data on the strength of slabs of monolithic brick pavements, see Engineering Record, 
Vol. 73 (1916), p. 86; and Engineering News-Record, Vol. 79 (1917), p. 820-23. 



538 BRICK PAVEMENTS [CHAP. XVII 

Since the practicability of laying the brick in a bed of cement 
mortar has been demonstrated, it has often been proposed to reduce 
the total depth of a brick pavement having a mortar bedding-course 
and cement-filled joints. In support of the possibility of making 
thinner pavements when the wearing coat is cement-grouted, it is 
often cited that 4-inch concrete roads in California give at least fair 
satisfaction; and that many, perhaps most, concrete roads in the 
Mississippi Vallej^ are only 6 inches thick. Some engineers have 
reduced the thickness of the concrete foundation, and others have 
reduced the thickness of the wearing coat. 

The extreme of the former practice is perhaps in Stockton Town- 
ship, VermiUon County, Ilhnois, in which in 1916 6i miles of rural 
brick roads were constructed with a brick wearing coat 4 inches 
thick and a concrete base only 1 inch thick. Another striking 
example is in Polo, Illinois, where in 1917 4-inch bricks were laid on 
2 inches of concrete. The purpose of either the 1-inch or 2-inch 
concrete in the above examples is not to act as a foundation to sup- 
port either the brick or the load upon the pavement, but to make a 
smooth surface on which to set the brick and also to prevent the grout 
filler from penetrating the subgrade. In both of the above examples 
the subsoil is clay or loam. 

An example of the practice of reducing the depth of the brick is 
to be found in many cities in the Mississippi Valley west of the river, 
in which many pavements were built between 1912 and 1917 using 
vertical-fiber brick 2J inches deep. Another example of the use of 
2j-inch brick is the driveway entrance to the Pennsylvania Passenger 
Station in New York City (§ 981). The wear on a grout-filled brick 
pavement is very small (see Fig. 193, page 528) ; and hence a brick 
2 J inches deep will last nearly as long as a brick 4 inches deep. 

An example of reducing the thickness of both the foundation and 
the wearing coat, is over 50 miles of rural brick roads in Florida 
consisting of 3j-inch grouted brick laid on puddled native sand; 
and similar pavements are laid on the streets of several southern 
cities. Some of these pavements have been in service two years, 
and have carried 10-ton motor trucks without any signs of distress. 
Of course, these pavements are not subjected to frost action. 

1029. It is impossible to compute or otherwise determine in 
general the permissible minimum thickness for any particular form 
of construction, since the required thickness varies greatly with the 
character of the subsoil and the climate; but it is certain that under 
conditions where a sand-cushion brick pavement gave fairly satis- 



ART. 2] CONSTRUCTION 539 

factory service, a thinner pavement may be used if it is built mono- 
lithic. Only considerable experience will determine the safe and not 
extravagant thickness of a pavement. 

1030. Of course, the cost will vary with the thickness; and 
whether it is cheaper to diminish the thickness of the concrete base 
or that of the brick-wearing course will depend upon conditions. 
There are localities where it is economical to decrease the depth of 
the brick, as for example where bricks are expensive and materials 
for concrete are cheap; and on the other hand, there may be con- 
ditions under which it is wiser to decrease the thickness of the con- 
crete. 

1031. Time under Construction. One of the most important 
advantages of the monolithic type of brick pavement is the length 
of time required for construction. All parts of it (the concrete 
foundation, the bedding course, and the grout filler) are constructed 
and seasoned simultaneously. With a concrete foundation, sand 
cushion, and grout-filled joints, the concrete foundation should 
be allowed to set for about 20 days before the sand cushion is spread 
and the brick set (see § 464) ; and another 20 days should be allowed 
for the cement grout to harden. This is one reason why a grout 
filler is not used more frequently. 

1032. Cost. The cost of construction of the monolithic type is 
10 to 12 cents per square yard less than that of the sand-cushion 
grout-filled type. The reasons for this difference of cost is as fol- 
lows: 1. All parts of the work are done at substantially the same 
time, and hence so much care is not required in protecting and caring 
for the work while the cement sets. 2. A lighter roller is used in 
rolling the brick. 3. Less sand is used for the bedding course. 
4. There is less risk of having to take up and re-lay brick on account 
of the sand cushion having been rained on. 5. It is possible to use 
either a thinner concrete foundation or a shallower brick. 6. For 
a rural road the monolithic construction does away with the need 
of a curb or edging. 

1033. Conclusion. In all points the monolithic pavement is 
superior to any other type of brick pavement. 

1034. PAVEMENT ADJACENT TO TRACK. It is exceedingly 
difficult to construct any pavement adjacent to a street-railway 
track that will not need frequent and extensive repairs. A large 
part of the difficulty is due to the fouodation of the track, which 
subject has been considered in Art. 3, of Chapter XV — Foundations 
for Street-railway Tracks. Another difficulty is in keeping a water- 



540 



BKICK PAVEMENTS 



[chap. XVII 



tight joint between the head of the rail and the pavement. Fig. 196 
shows the standard practice of laying brick in the track area when 



9"Rail 



'Morfarbecf 



■^Bituminous ,„ 
filler SJorTcf ^Vifrifiedb/ocMS-. 






.- i:o.--.f::,-.a-..;-.'.-7-.v: ;•:... ;< 

^•o-:f;;::-A?:;^r^:.r.i;:--:?^;; i 



iu?-7-v-'--p--.y-p-.-..;y'-:^e-|.^&l 
Concrefe^ 



Fig. 196. — Standard Practice in Baltimore, Md. 



a grooved rail is used; and Fig. 197 shows the corresponding 
arrangement when a T rail is used. Most brick manufacturers 



. w^Wf \ I |"1K~I — 1/ I I — I — r"^ I I I — r — 

''>///i°j))y/'}'J 6"^d"^ 7-0" iVhifie Oak Tie W^^0!^ 



3c7nd and , 
Cement /: 






7o> 



Jubg/xde- 



bricH- 




FiG. 197. — Standard Practice of Fort Wayne and Wabash Vallet Traction Co. 



make the " bull-nose ^* brick for placing next to the inside of the 
rail as shown in the upper view in Fig. 197. Notice in the lower 
part of Fig. 197 that the paving between the rails is level with 
the top of the rails; but often it is made level a little below the top 
of the rail. Notice also that the lower half of Fig. 197 has a longitu- 
dinal concrete beam under each rail. 

Bricks are much used for paving the railway area, particularly 
between the rails, because of their low first cost and of the ease with 
which they can be laid. ^. | 

It is practically impossible to maintain a brick pavement with a 
sand cushion adjoining a railway track, since the cushion will shift 
under travel and since water will leak into the cushion and freeze. 

1035. MAXIMUM Permissible Grade. The Committee of 
the American Society of Civil Engineers recommends 12 per cent 
as the permissible maximum grade for a brick pavement with a 



ART. 2] CONSTRUCTION 541 

bituminous filler, and 6 per cent for a grout filler — see Table 15, 
page 58. The report impliedly recommends the use of a plain brick 
and bituminous filler on steep grades; but this is not in accordance 
with accepted good practice. The best practice employs grout on all 
grades; and uses plain brick on grades up to 5 or 6 per cent, and 
hill-side brick (§ 936) for grades up to 10 or 12 per cent. Hill-side 
brick and grout filler have given fair satisfaction on grades as high 
as 15 and 18 per cent. 

1036. Streets Paved with Brick. The preceding discussion 
of brick pavements has been without special reference to either city 
streets or country roads. A few differences resulting from the dif- 
ferent locations of the pavement remain to be considered. 

The chief difference in the construction of a brick pavement on a 
city street and on a rural road is due to the fact that usually the 
paved portion is wider on the former than the latter. This neces- 
sitates either the use of a longer template in striking the concrete 
foundation and the bedding course, or the placing of screeds and the 
use of a shorter template. The construction of the concrete founda- 
tion has been discussed in Chapters VII and XIV. The template 
employed in striking the concrete is described in § 460, and that used 
for the bedding course in § 972.* 

The bricks are usually transported from the parking to the setter 
either b}^ hand with pallets or tongs, or by a roller gravity conveyor 
— usually the latter. 

Longitudinal expansion joints are always required for street 
pavements. 

1037. Roads Paved with Brick. The foundation for brick 
pavements on rural roads more frequently than on city streets is an 
old macadam road (§ 437). 

Formerly brick roads usually had a sand cushion, but recently 
the semi-monolithic or monolithic construction is ordinarily em- 
ployed — generally the latter. Fig. 198 shows two typical views of 
the construction of a monolithic brick road. The left-hand view 
shows the bricks, the fine and coarse aggregate, and the cement 
delivered ready for work, and also the side forms in place. Notice 
that the materials have been transported to the job on an industrial 
railway. The right-hand view shows work in progress. In the lat- 
ter notice the steel side-forms, and the tamping template. The 
double template (§ 982) is shown between the tamping template 

j* For an illustrated account of the laying of a monolithic brick pavement 33 feet wide on a 
city street, see Engineering News, Vol. 76 (1916), p. 978-79. 



542 



BRICK PAVEMENTS 



[chap. XVII 



and the concrete mixer, and is weighted down with bags of 
cement. 

Formerly the sand-cushion brick road was built with an inde- 
pendent curb (§729-34), or with an integral curb or an edging 
(§ 771). Fig. 199 shows the concrete foundation for a sand-cushion 




Fig. 198. — Construction of Monolithic Bbick Road. 




Fig. 199. — Concrete Foundation with Edging. 



brick road with edging, in process of construction. The concrete is 
being spread to grade with shovels and smoothed with the back of a 
shovel. The surface on the concrete slab is not first-class; but is 
good for the method used, and is good enough in consideration that a 
sand cushion is later to be used. The combined curb and gutter 



ART. 2] 



CONSTRUCTION 



543 



(of the shallow V type) is completed on the far side, and the form for 
the integral edging is in position in the foreground of the left side. 
The trussed, scantling or template is being used in testing the crown 
or elevation of the concrete, the ends of the projecting strip indicating 
the height the concrete should have. 

Fig. 200 shows four views of a semi-monolithic brick road 
with edging, in process of construction. In view 1, notice the 
low spot in the sand-cement bed. In view 2, notice that the men 
are walking on the ungrouted brick, which is objectionable, but less 
so with a cement-sand bed than with a sand-cushion (§ 971). In 




1. Striking the Sand-cement Bed. 



2. Laying the Bricks. 




3. Sprinkling the Brick. 4. Second Application of Grout. 

Fig. 200. — Construction of Monolithic Brick Road with Edging. 



view 3, the stream of water is so solid or heavy as to wash out the 
cement in the bedding layer, although the laborer says the stream 
does no harm as he always plays upon the center of a brick. View 4 
shows the mush-like consistency of the last coat of grout, which is 
dangerously near being too thick to run into the joints well. 

1038. Since the introduction of the monolithic brick pavement, 
the brick wearing-coat for rural roads is laid without any curb or 
edging (§471), experience having shown that the bricks at the edge 
of the pavement are not dislodged by traffic. 



544 BRICK PAVEMENTS [CHAP. XVII 

The edge or corner of a monolithic brick road is rather rough and 
ragged, and very destructive of automobile tires in turning off and 
onto the pavement, if the earth is not kept well filled up against the 
pavement. It is nearly impossible to keep the earth shoulders full, 
and gravel or broken-stone shoulders are seldom used; and hence 
this ragged edge is an objection to omitting the concrete edging. 
This objection could be eliminated by laying a bull-nose brick (see 
§ 1034) at the end of a course; but it is not known that this has ever 
been done. The outer corner of the concrete edging can be readily 
rounded off with an edging tool, although it is not often so done. 

1039. Cost of Brick Pavements. The cost will vary with the 

locality and the details of construction, and consequently any gen- 
eral statement of cost will be only approximately true for any par- 
ticular case. 

The grading is usually done by the cubic yard; and the cost 
varies with the character of the soil, the depth to be removed, the 
length of haul, etc. The cost of grading ranges from 15 to 50 cents 
per cubic yard; but in easy soil and moderate cuts, it generally 
varies from 25 to 35 cents. It usually costs 3 to 5 cents a square 
yard to dress off the subgrade after it has been graded with drag 
or wheel scrapers, and to throw the material into wagons. 

The cost of rolling the subgrade will depend upon whether it is 
rolled longitudinally only, or both longitudinally and transversely. 
With a self-propelled roller the cost of rolling, both transversely and 
longitudinally, will be about 0.6 cent a square yard, exclusive of 
interest, storage, and depreciation of the roller. 

The cost of the concrejbe foundation will vary with the price of 
cement, the proximity of broken stone or gravel, the character of the 
concrete, etc. Ordinarily the materials for a 6-inch course will cost 
50 to. 60 cents per square yard, and the labor 6 to 8 cents per square 
yard. 

The price of bricks will vary with their size, the locality, and the 
freight rate. Previous to 1916 there was no uniformity in size, 
common sizes for the wearing face being 3J by 8J inches, 3f by 8, 
and 3 by 9; and some brands requiring 42 for a square yard, some 40, 
and some 38. Since the beginning of 1916 there has been a vigorous 
attempt to have all paving bricks of standard size, or rather to have 
the wearing face 3 J by 8 J inches, of which 40 make a square yard of 
pavement. In 1915, before the disturbance of prices due to the 
Great European War, the average price at the plant for standard 
blocks 4 inches deep was about $15.00 per thousand, or 60 cents per 



a 



ART. 2j CONSTRUCTION 545 

square yard; but in 1917 for various reasons the price was practically 
50 per cent more. There is no difference in price between wire-cut 
lug and re-pressed bricks. In estimating the freight it may be 
helpful to know that a brick 2 J X 4 X 8| inches weighs about 7 
lb., and a block 3i X 4 X 8^ inches about 9.75 lb. In estimating 
freight, the fact should not be overlooked that for one reason or 
another a considerable number of bricks are rejected. With careful 
grading at the kiln the broken and rejected brick is likely to be 1 to 2 
per cent. 

In the early history of brick paving it was customary for the 
contractor to buy brick by the thousand ; but the contractor claimed 
that the manufacturer did not cull the brick sufficiently carefully 
at the kiln, and consequently the rejections on the job were unduly 
great. For a time it became customary to buy the brick f.o.b. 
destination at a stated price per square yard in place in the pave- 
ment; but under this plan, the manufacturer claimed that the con- 
tractor did not use proper care in handling the bricks, did not keep 
them clean, used good brick instead of chipped or broken brick in 
making closures, and left good bricks along the finished pavement. 
At present it is customary to sell the brick by the thousand f.o.b. 
destination. The usual price is $25.00 per thousand f.o.b. destina- 
tion. 

The cost of hauling and piling on the side of the street is about 
$1.50 per thousand for a haul of 1 mile, of which sum about half is 
the cost of loading and unloading, and half the cost of team and 
driver; but this cost for team and driver necessitates the use of three 
wagons with each team. 

The cost of setting blocks of which 40 make a square yard varies 
from 4 to 6 cents per square yard. 

The cost of turning the chipped brick and replacing the rejected 
ones will depend mainly upon the severity of the inspection and upon 
the degree of care employed in culling the brick before they are laid. 
In a particular case, 80 hours were required to turn the chipped 
blocks and to replace the rejected blocks with good ones, in 1,633 
square yards of pavement, or, say, 1 hour for each 20 square yards. 
The blocks were 3X4X9 inches, and about 2 per cent were 
turned and about 2 per cent were rejected. 

For data concerning the cost of sand filler, see § 995; for cost of 
cement filler, see § 1006; and for cost of bituminous filler, see § 1013. 

Examples of the actual cost of brick pavements are given in 
§ 1041-48. 



546 



BRICK PAVEMENTS 



[chap. XVll 



1040. In this connection it should not be overlooked that the 
cost of the pavement proper is usually not the only cost of improving 
the street when it is paved. For details see § 878. 

1041. Examples of Cost. In the following examples an attempt 
has been made to present the data in such detail as to make clear 
the form of construction; but unfortunately it is not always possible 
to present information concerning important economic conditions, as 
freight rates, the condition of the wagon roads over which material 
is hauled, efficiency of labor, etc. 

1042. Sand-cushion Asphalt-filled Brick Pavement. Table 56 
gives the details of laying a brick pavement. The excavation was 
done with a Maney 4- wheel scraper (§ 154) and a 20-H.P. tractor. 
Wages were as follows: Common labor 20 cents per hour; brick 
setters, 55 and 40 cents; engine runner for concrete mixer, 30 
cents; team, wagon, and driver, 50 cents per hour. 

TABLE 56 

Cost of Sand-cushion Asphalt-filled Brick Pavement 

In Central Illinois in 1916 



Items. 



Cost Per Sq. Yd. 



Partial. Total. 



Subgrade : 

Rough grading at 29.8 cts. per cubic yard . 
Surfacing and rolling with 10-ton roller. . . 



Concrete Foundation, 6 inches of 1 : 3 : 5 : 

Labor at 20 cts. per hour 

Cement at $1.48 per barrel (net) on job. . . 

Gravel at $1.40 per cubic yard on job 

Sand at $1.50 per cubic yard on job 

Coal and water 



Sand Cushion, IJ inches thick 



Brick, wire-cut lug, 3|X4X8^ inches: 
Purchase price, f .o.b. destination .... 

Handling in car 

Hauling to street — average 2,200 feet. 
Laying, contract price 



Joint Filler: 

Asphalt, 12 lb. per square yard. 
Labor, heating and pouring. . . . 



Miscellaneous Expense 



Total cost, exclusive of administration, tools and profits . 



$0,137 
.040 



.056 

.227 
.156 
.122 
.006 



.807 
.027 
.020 
.050 



095 
,060 



$0,217 



.568 
0.640 

.904 

.155 
.052 



$1,960 



ART. 2] 



CONSTRUCTION 



547 



1043. 3-inch Brick Pavement. Table 57 shows the cost of a 
brick pavement having a 4-inch concrete foundation, IJ-inch sand 
cushion, 3-inch vertical-fiber brick wearing coat, and asphalt joint- 
filler. 

TABLE 57 
Cost of 3-inch Brick Pavement in Falls City, Neb., in 1914* 



Items. 



Cost Per Sq. Yd. 



Partial. 



Total. 



SUBGRADE : 

Rough grading 

Surfacing and rolling. 



$0.03 
.015 



Concrete Foundation, 4 inches thick: 

Cement at $1.63 per barrel 

Stone at $2.25 per cubic yard 

Sand at $1.10 per cubic yard 

Mixing and placing 



0.185 
.232 
.060 
.050 



Sand Cushion, 1| inches, at $1.10 per cubic yard. 



Brick, vertical-fiber, 3 inches deep, f.o.b destination. 

Unloading and hauling 

Preparing cushion and setting brick 

Rolhng 



0.70 
.05 
.04 
.006 



Joint Filler: 

Bituminous material. 
Applying 



0.12 
.03 



-Incidental Expenses. 



$0,045 

.527 
.046 

.796 

.150 
.017 



Total, exclusive of administration, depreciation, and profits. 



$1,581 



* Engineering News, Vol. 73 (1915), p. 223. 

1044. Brick Roads in New York. Table 58, page 548, shows the 
average cost of a great number of brick roads built in New York 
by the State Highway Commission in 1912 and 1913.* The roads 
were 15 feet wide, had 5-inch concrete base, 6-inch concrete edging, 
sand cushion, and grout filler. The cost below includes engineering 
expenses. 

1045. Monolithic Pavement. Table 59, page 548, shows the labor 
and materials required for a monolithic brick pavement 33 feet wide, 
with 4-inch brick, and 1-inch special expansion joints every 82 feet. 
Table 60, page 548, shows the labor cost of this job. 



* Engineering News, Vol. 70 (1913), p. 1149. 



548 



BRICK PAVEMENTS 



[chap. XVII 



TABLE 58 
Average Cost of Brick Roads in New York in 1912 and 1913 



Items. 



Total Cost. 



Per Cent. Per Mile. 




Excavation 

Drainage structures 

Subgrade and foundation 

Brick wearing-course and edging . 
Minor expenses 

Total 



100.0 



$2 200 

700 

6 300 

14 700 
500 



$24 400 



TABLE 59 

Amount of Labor and Materials for Monolithic Brick Pavement* 

Central Illinois, 1916 



Labor. 


Hours per 
Sq. Yd. 


Materials. 


Cu. Ft. Per 
Sq. Yd. 


Base and Bed: 

laborers 


0.2305 
.0154 
.0138 

.1772 
.0227 

.0887 
.0048 

.0171 
.0171 
.0171 


Concrete Base, 4 inches: 
1 : 6 cement 


5 


engine runner 


gravel 

Bedding Mortar, |-inch: 
1 : 2 cement 


3 000 


sub-foreman 




Brick Setting: 


.094 


laborers 


sand 


.188 


setters 


Grout, 1:1: 

cement 




filling joints 


.144 


spreading sand 


sand 


.144 


Overhead : 

timekeeper 


Top Covering: 

sand 


.188 


foreman 






water boy 









TABLE 60 

Cost of Labor for Monolithic Brick Pavement* 

Central Illinois, 1916 



Items. 

Concrete base, 4 inches of 1 : 6 gravel, 

Setting brick, 3|X4X8| inches 

Fining joints with 1 : 1 grout 

Spreading top covering of sand 

Total cost of labor 



Cost 
Per. Sq. Yd. 



$0.0649 
.0525 
.0244 
.0011 



$0.1429 



*[ Engineering News, Vol. 76 (1916), p. 1219. 



ART. 2] CONSTRUCTION 549 

1046. Brick on Old Macadam. Table 61 shows the cost of 
laying a new brick pavement on an old macadam base by the Street 
Department of Carlisle, Pa. The macadam was spiked with a 13-ton 
3-wheel self-propelled roller, excavated to subgrade, surfaced with 
hand picks, and rolled. The bricks were rolled with a 5-ton roller 
drawn by 12 men. 

Table 61 
Cost of New Brick Pavement on Old Macadam Foundation* 



Items. 



Grading and rolling subgrade 

Placing 5 inches of concrete in pipe trenches . 

Cushion course, — limestone screenings 

Brick f.o.b. destination 

Unloading and hauhng brick 

Laying brick. 

Rolling brick by manual labor 

Grouting joints 

Expansion joints, longitudinal and transverse . 
Top coating of sand 

Total 



Cost 
Per Sq. Yd. 



$0.1126 



.0543 
.8600 
.0777 
.0376 
.0062 
.0845 
.0353 
.0047 



$1.3587 



* Engineering News, Vol. 72 (1914), p. 1263. 

1047. Semi-monolithic Brick on Old Macadam. Table 62, page 

550, shows the cost of laying a semi-monolithic brick pavement on 
an old macadam road. A 2-inch dry 1 : 4 mixture of cement and 
sand was used for the bedding course. The water cost nothing 
except the piping. The self-propeUing roller used on the subgrade 
was loaned, and no charge therefor is included. Common labor 
received 20 cents per hour, and team and driver $6.00 per day. 

1048. Cost in Various Cities. Table 63 and 64, page 550 and 

551, shows the cost and several details of 3-inch and 4-inch brick 
pavements in various cities. A few cities use 3j-inch brick, and a 
few 2i-inch ; but none of these are given here. 

1049. Merits of Brick Pavements. Bricks as a paving 
material have some attractive features. 1. .They may be had in 
small units of practically uniform size. 2. They may be had in 
large or small quantities. 3. They may be laid rapidly without 
special expert labor. 4. When ailing pipes or other causes neces- 
sitate the disturbance of the pavement, ordinary tools and intelli- 
gence can restore the original surface. 5. Brick pavements give a 
good foothold for horses, 6. They do not wear sKppery. 7. They 



550 



BRICK PAVEMENTS 



[chap. XVII 



TABLE 62 

Cost of Semi-monolithic Brick Pavement on Macadam* 

Alton, Illinois, 1915 



Items. 



Cost per Sq. Yd. 



Partial. Total 



Labor : 

Grading, setting forms, building barricade . 

Placing mortar bed and laying brick 

Mixing and applying 1 : 1 grout filler 



Brick: rattler loss 25% 



Mortar Bed: 

Sand— 0.083 ton at $0.82 

Cement— 0.079 barrel at $1.35. 

Grout Filler: 

Sand— 0.008 ton at $0.82 

Cement— 0.036 barrel at $1.35, 



Materials for Forms: 

Lumber at $20 per M — salvage at 67* 



Template. 
Stakes and nails. 



Miscellaneous: 

Depreciation on small tooh and water line, teaming, etc , 

Cleaning Up 

Total, exclusive of administration and profits 



$0,084 
.087 
.027 



.068 
.105 



.007 
.047 



.009 
.008 
.002 



$0,198 
.560 

0.173 

.054 

0.020 

0.038 
.017 



$1,060 



* Engineering Record, Vol. 73 (1916), p. 414. 



TABLE 63 
Cost of 3-Inch Brick Pavements in Various Cities in 1916 * 



Locality. 


Sq. Yd. 
Laid in 
1916. 


Foundation. 


Bed Course. 


Filler. 




State. 


City. 


Thick- 
ness, 
inches. 


Propor- 
tions. 


Thick- 
ness, 
inches. 


Kind.t 


Kind.t 


Propor- 
tions. 


Cost 

Per 

Sq.Yd. 


Kansas 

Missouri. . . . 
Nebraska. . . . 


Arkansas City. 

Ottawa 

Parsons 

Salina 

Topeka 

Sedalia 

Fremont 


26 132 
14 000 

6 208 

27 461 
46 000 
12 345 
20 809 


4 
4 
4 
5 
5 
4 
4 
5 
5 
6 
5 


1:2:5 
1:3:5 
1:3:5 

r:"2i:'5 

1:3:6 

1:3:5 

1:3:6 

1:3:5 

1:3:6 

1:3:6 


If 

2' 

' ' ' 3 ' ' 

ll 


S 
S 

S 

s 
s 
s 

s 

M 
M 

s 


A 
A 
A 
A 
A 
A 
A 
A 
G 
A 
A 


' 1 :'3" ' 


$1.81 
1.57 
1.63 
1.92§ 
1.7711 
1.66 
2.04 
1 95 


Oregon 

Texas 


Astoria 

Houston 

San Antonio . . 


3 418 
17 500 
41 571 


2.7011 

2.45 

2.50 



* Municipal Engineering, Vol. 52 (1917), p. 128-30. 
t S = sand; S-C = sand-cement; M= mortar. 
J A = asphalt; G = grout. 



§ $2.15 with 4-inch re-pressed brick. 
II $1.97 with 4-inch re-pressed brick. 
II 2f-inch brick, 



ART. 2] 



CONSTRUCTION 



551 



TABLE 64 
Cost of 4-Inch Brick Pavements in Various Cities in 1916 * 



Locality | 




Foundation. | 


Bed Course 


Fx! 


.LER. 1 








Sq. Yd. 
Laid in 














Cost 


















Per 


State. 


City. 


1916. 


Thick- 
ness. 


Propor- 
tions. 


Thick- 
ness. 


Kind.t 


Kind.t 


Propor- 
tions. 


Sq. Yd 


California. . . 


Los Angeles. . . 


1 800 


4" 


1 : 3 : 6 


1 . 5-2" 


S 






$2.52 


Illinois 


Alton 


51 510 


4 


1:3:6 


1 


s-c 


G 




1.65 




Champaign. . . 


30 000 


6 


1:3:5 


li 


s 






1.81 




Danville 


42 000 


5 


1:3:5 


1 


s-c 


G 


1 : 1 


1.72 




Galesburg .... 


17 760 


4 


1:3:6 


1 


s 


A 




1.76 




Mattoon 


32 269 


5 


1 :4i : 8 


1 


s 


G 


1 : 1 


1.63 




Peoria 


36 536 


4-5 


1:3:5 


1-2 


s 


G 


1 : 1 


1.60 


Indiana 


Crawfordville 


4 108 


4 


1:3:5 


li 


s 


G 


1 : 1 


1.30 




Ft. Wayne 


21005 


6 


1:3:6 


2 


s 


G 




1.79 




Muncie 


12 000 


6 


1:3:6 


2 


s 


G 


1 : 1 


2.03 




New Castle. . . 


19 408 


5 


1:3:6 




s-c 


G 


1 : 2 


1.60 




Wabash 


2 575 


6 


1:3:6 


li 


s 


G 


1 : 1 


2.25 


Kansas 


Leavenworth. . 


4 717 


5 


1:3:5 


2 


s 


G 


1 : 1 


1.80 


Kentucky. . . 


Louisville 


59 758 


6 


1:3:6 


li 


s 


G 


1 : 1 


1.81 


Mass 


Fitchburg .... 


13 844 


5 


1:2:4 


1 


s 


G 




2.77 


Michigan. . . . 


Detroit 


71 800 


6 


1:3:6 


1 


s 


G 




2.14 




Grand Rapids . 


34 512 


5 


1 :3i : 7 


U 


s 


G 


1 : 1 


1.90 




Port Huron. . . 


2 572 


5 


1:2:5 


1 




G 


1 : 2 


1.94 


New York . . . 


Amsterdam. . . 


4 310 


6 


1:3:6 


1 


M 


G 




2.50 




Jamestown. . . 


19 947 


5 


1 :6 


u 


s 


G 


1 : 1 


2.08 




Poughkeepsie . 


25 000 


5 


1:3:6 


1 


M 


G 


1 : 1 


2.16 


Ohio 


Canton 


50 120 


5 


1:3:5 


1 


s 






1.60 




Findlay 


34 637 


6 


1:3:5 


n 


s 


G 


1 :n 


1.74 




Lakewood . . . . 


22 223 


6 


1:3:6 


u 


s 


G 


1 : 1 


1.82 




Toledo 


63 121 


6 


1 :3| :6 


1 


M 


A 




2.04 




Warren 


42 000 


5 


1:3:6 


2 


s 


G 


1 : 1 


1.80 




Youngstown . . 


42 333 


6 


1:3:6 


2 


s 


G 


1 : 1 


2.10 


S. Carolina. . . 


Greenwood . . . 


15 000 


4 


1:3:6 


u 


s 


G 


1 : 1 


1.95 


Washington. . 


Seattle 


112 581 


5-6 


1:3:6 




s-c 


G 


1 : li 


2.55 


Wisconsin. . . 


Beloit 


14 488 


5 


1:3:6 


ll 


s 


A 




1.99 




Racine 


30 326 


5 


1:3:5 


2 


s 


G 




2.15 



* Municipal Engineering, Vol. 52 (1917), p. 128-30. 
t S = sand; S-C = sand-cement; M = mortar. 
J A = asphalt; G = grout. 

are adapted to all grades. 8. They have low tractive resistance, 
particularly if the joints are filled with cement grout. 9. They are 
not specially noisy when properly laid. 10. Brick pavements yield 
no mud or dust. 11. They are easily cleaned. 12. If the joints 
are filled with sand, they are only slightly absorbent; and if filled 
with hydraulic or bituminous cement, they are non-absorbent. 13. 
Brick pavements have a pleasing appearance. 14. They are very 
durable, particularly if the joints are filled with cement grout. 15. 
Thej^ are cheap in consideration of their small cost of maintenance 
and long life. 

1050. Specifications. The American Society for Testing 
Materials publish specifications for the standard rattler, the standard 
rattler test, and paving brick, copies of all of which can be had for a 
nominal sum of the Secretary. The American Society of Municipal 
Improvements publish complete specifications for brick street pave- 
ments having sand bedding course, and grout or tar or asphalt filler, 



552 BRICK PAVEMENTS CHAP. XVII 

copies of which may be had for a nominal sum of the Secretary. 
The National Paving Brick Manufacturers Association pubhsh com- 
plete specifications for all varieties of brick paving for both streets 
and roads, using wire-cut lug or re-pressed brick, copies of which 
may be had gratuitously of the members of the Association and of the 
Secretary, Brotherhood Building, Cleveland, Ohio. The Western 
Paving Brick Manufacturers Association publish specifications for 
all varieties of brick paving including the use of vertical-fiber brick, 
copies of which may be had gratuitously of members of the Asso- 
ciation, or the Secretary, D wight Building, Kansas City, Missouri. 
The Dunn Wire-cut Lug Brick Co., Conneaut, Ohio, an organization 
to promote the use of wire-cut lug brick by securing good and eco- 
nomical brick pavements, publish a complete set of specifications 
for wire-cut lug brick-paving, which may be had gratuitously. 
Many of the State Highway Commissions pubhsh complete speci- 
fications for brick paving, which can doubtless be had gratuitously 
by residents of the respective states. 

Art. 3. Maintenance 

1052. The maintenance of pavements has never received atten- 
tion in proportion to either its economic importance or the comfort 
of the user. This is particularly true of brick pavements, partly 
because they are comparatively new, and partly because the 
material not being subject to decay the need of maintenance has 
been over-looked. There has been no comprehensive diagnosis of 
the diseases of brick pavements, nor have any effective remedies 
been developed. 

1053. REPAIRS OF Brick Pavements. The more common 
matters that need attention in the maintenance of brick pavements 
are: (1) holes due to soft brick, (2) depressions due to shrinkage or 
flow of the sand cushion, (3) depressions due to sinking of founda- 
tion, (4) depressions due to settlement of trenches, (5) defects at 
transverse expansion joints, (6) defective grouting, (7) bulges, 
(8) longitudinal cracks, (9) re-laying pavements in patches and cuts, 
and (10) re-surfacing worn pavements. 

1054. Soft Brick. A soft brick in the pavement wears away and 
makes a hole. Each wheel, particularly a steel-tired one, dropping 
into the hole crushes and chips the adjoining bricks even though 
they are hard, and the hole gradually increases in size and depth. 
When such a brick shows itself it should be cut out and be replaced 



ART. 3] MAINTENANCE 553 

with a good one. The defective brick must be cut out with a chisel 
and hammer, the joints adjacent to it must be cleaned, and the bed- 
ding course must be removed. If the bedding course is sand, it 
must be carefully compacted; and if it is mortar, a new bed must be 
laid. After the new brick has been placed and firmly settled into the 
bedding course, and found to conform to the general surface of the 
pavement, the joints should be filled. If the joint filler is grout, 
the new brick should be dampened before the grouting is done, and 
care must be taken to see that the sand cushion has not pushed up 
into the joint; and after the joint is filled, the spot should be bar- 
ricaded until the cement has set. 

The patch should be barricaded for at least a day or two. Theo- 
retically, this time is far too short for the cement grout to gain its 
full strength; but experience seems to show that a day or two is 
reasonably safe. The explanation of this anomalous result is that 
the spot being small, there is not much probability that a wheel 
carrying a maximum load will go over the spot until the cement 
grout has gained sufficient strength to hold it. Obviously then, 
the denser the traffic or the heavier the loads, the longer the barri- 
cades should remain. 

If the brick are not quite uniform in quality, there may be so 
many soft bricks as to make it impracticable to remove each soft one, 
in which case the pavement must continue in service until it is re- 
surfaced as described in § 1063, 1068, or 1069, or until it is replaced 
with a new pavement. The possibility of this condition arising is 
the reason for making the rattler test in such a way as to secure 
information as to the uniformity of the brick; and is also a reason 
for carefully inspecting the bricks after they are laid. 

1055. Shrinkage of Sand Cushion. A common defect of brick 
pavements having a sand cushion is the shrinking of the cushion 
away from the brick, due probably to the sand being wet when the 
bedding course was spread. If the joints are filled with sand, the 
first evidence of the shrinkage of the cushion is a shallow saucer-like 
depression of the surface of the pavement. The remedy is to take 
up the low spot and re-lay the sand cushion. If the spot is not 
repaired, the depression is likely to be enlarged by the impact of 
passing wheels and the flow of the sand cushion. The flow of the 
sand cushion sometimes gives rise to broad shallow ruts, particularly 
on a street having a street-car track, since then the travel is con- 
centrated on a narrow strip. 

If the joints between the bricks are filled with cement grout, the 



554 BRICK PAVEMENTS [CHAP. XVn 

first evidence that the sand cushion has shrunk away from the 
brick is a rumbhng noise when a steel-tired wheel goes over the 
spot. Tapping the surface of such a pavement with a hammer will 
reveal many such hollow spots. Such spots finally break down by 
the shearing of the joint filler. After this is done, water enters 
through the broken joints, and freezing Ufts the pavement; and 
sometimes breaks other joints, and perhaps tilts a portion of the 
pavement and thereby roughens the surface. The examination of 
any sand-cushion pavement after it has been in service a year or 
two, will show a number of such breaks. The only remedy for this 
defect is to cut out the low spot and re-lay it. Many old pave- 
ments have so many such breaks that it is impracticable to repair 
them. The adequate preventive is not to use a sand cushion, or at 
least not a thick one. For a discussion of the method of resurfac- 
ing a brick pavement, see § 1063, 1068, or 1069. 

1056. Settlement of Foundation. Sometimes a round depression 
is due to the settlement of a spot of the subgrade. It can not always 
be determined from a surface examination whether the defect is due 
to the shrinkage of the sand cushion or the settlement of the sub- 
grade. To determine the cause, remove the wearing coat and the 
bedding course, and examine the top of the foundation for a crack 
near the edge of the depression. If the foundation is broken, it 
should be taken out, and the cause of the settlement be sought for. 
Perhaps it is due to lack of consolidation at the time of construction, 
or perhaps it is due to a leaking pipe or a spring. If it is due to the 
first, the remedy is thorough tamping; if to a leaky pipe, the remedy 
is obvious; and if to a spring, then adequate drainage must be pro- 
vided. After the causes have been removed, the pavement must be 
replaced as described in § 1061. 

1057. Settlement of Trench. The settlement of the back-filling 
of a trench is one of the most common and most serious defect in 
pavements. The settlement over a longitudinal trench is more 
noticeable but less damaging than that over a transverse trench. 
The prevention during construction is discussed in § 764-70. 

When a pavement sinks over a trench, it is difficult to eliminate 
the defect. The first step is to remove in succession the wearing 
coat, the bedding course, and the foundation. The second step is 
to consolidate the back-filling; but this is not easily done. During 
construction, if the trench is not too deep and if it was not back- 
filled under very unfavorable conditions, the back-filling can usually 
be consoUdated fairly well by rolHng (§ 763) ; but this is impracticable 



ART. 3] MAINTENANCE 555 

after the pavement is laid. Under some conditions flooding (§ 766) 
may be worth trying. The most feasible way is to dig out the trench 
and replace the material with adequate tamping (§ 767-69). The 
usual method is simply to fill the trench, generally a little more than 
full, and re-lay the pavement, allowing it to be a little high with the 
expectation that it will settle to place. But sometimes the pave- 
ment does not settle, and sometimes it settles too much; and then 
in either case, another trial is needed to secure a good surface. 

Sometimes an attempt is made to remedy such a defect by laying 
a thicker concrete foundation over the trench and allowing the slab 
to extend laterally beyond the trench; but usually such a remedy 
is not effective except perhaps where the trench is comparatively 
narrow^ and where the banks of the trench are fairly sohd. A radical 
remedy would be to dig out the trench and fill it with sand, or gravel, 
or a very lean concrete (§ 770). The difficulty of removing this 
defect is a reason in favor of good original construction. 

For a discussion of the method of replacing the brick in making 
such a repair, see § 1061. 

1058. Transverse Contraction Joints. Transverse contraction 
joints are a common cause of deterioration in a brick pavement 
having grout filler. The action of the joint in damaging the adja- 
cent pavement has been explained in § 1019-20, and illustrated in 
Fig. 195, page 535. The only remedy in such cases is to remove 
the expansion joint and re-lay the pavement. For some hints con- 
cerning the method of re-laying the pavement, see § 1061. 

1059. Defective Grouting. Defective grouting is a cause of 
serious deterioration in a brick pavement. In a pavement with a 
rigid filler, it is essential that the filler extend from top to bottom of 
the joints, as otherwise the pressure due to the expansion of the pave- 
ment will be concentrated on one portion of the joint, which will 
crush the filler and break the bond, and cause the pavement to wear 
as though it were sand-filled ; or the pressure may cause the brick to 
spall or crush. There are two possible reasons for such defects: 1. 
The sand of the cushion course may have pushed up into the bottom 
of the joint when the bricks are rolled; and consequently the filler 
at the bottom of the joint will not be as rigid as that at the top. 2. 
The grout, particularly that of the second coat, may have been so 
thick as to bridge the joint and fill only the top of the joint. Fig. 201, 
page 556, shows a spot in which the grouting was defective. Notice 
that a rut has formed at the right of the defective spot, that a brick 
at the top of the spot is badly shattered, and that several bricks have 



556 



BRICK PAVEMENTS 



[chap. XVH 



spalled. These defective spots are usually small in the beginning, 
but they gradually enlarge owing to the increased effect of impact 
and also to the effect of the water that penetrates such spots. 




Fig. 201. — Defective Grouting. 



These spots may be cut out by hand with chisel and hammer, 
or with a pneumatic chisel or chipping hammer as shown in Fig. 202. 




Fig. 202. — Pneumatic Chisel Cutting out Defect. 

In Baltimore the cost of toothing out a brick pavement having 
grout filler (see Fig. 204, page 559) was 18 cents per hneal foot by 
hand, and 2.76 cents per lineal foot with a pneumatic chisel.* 

* Municipal Engineering, Vol. 52 (1917), p. 6. 



AET. 3] 



MAINTENANCE 



557 



In cutting out such a spot no half brick should be left, as other- 
wise there will not be sufficient bond between adjacent bricks. The 
joint-filler should be thoroughly cleaned from the edges of the toothed 
bricks, care being taken not to break the bond of the remaining 
bricks. The bedding course should be adjusted so as to bring the 
tops of the new bricks to the proper elevation. Care should be 
taken that the brick to be used in filling the patch are of exactly the 
same size as the old ones. The brick should be laid, tamped, and 
grouted as in the original construction. 

1060. Bulge. A bulge is a buckHng or heaving of the wearing 
coat of a brick pavement due to its expansion. Sometimes the bulge 
is simply a wave, sometimes a ridge having a crack at its crest, 
and occasionally an explosion or " blow-up " in which a number 
of bricks are thrown into the air with considerable force. Fig. 203 




Fig. 203. — Two Bulges in Brick Pavement. 



is a view of two upheavals. The right-hand example is a mild up- 
heaval, and the left-hand one is a moderate explosion. A bulge 
usually occurs at a crowned foot-way crossing or a street intersec- 
tion. Notice that both of the bulges shown in Fig. 203 occurred at a 
crowned foot-way crossing. 

If a main street is paved and its crown is carried through the 
intersection with another street and later the latter is paved, the 
pressure due to the expansion of the pavement of the cross street 
against the abutments of the crown of the main street may cause 
the crown of the arch to rise with or without an explosion. The 
mildest form of this phenomena is simply hfting the pavement from 
the sand cushion, in which case the pavement will give out a rumbling 
sound as a wheel passes over it, and it will come back to place when 
the pavement cools. Or the pavement may be cracked near the 



558 BRICK PAVEMENTS [CHAP. XVII 

middle of the main street, in which case the pavement must be re- 
laid along the crack, since the pavement will not of itself return to 
its former position. Upheavals or cracks from this cause can be 
prevented by putting in an expansion joint where the pavement of 
the cross street abuts against that of the main street. 

Sometimes a lateral pressure on the pavement will lift the crown 
from the sand cushion, as is shown by a rumbling when a vehicle 
goes over it; and in extreme cases the pavement will crack near the 
middle of the street. This lateral thrust may be due to an inadequate 
or obstructed expansion joint next to the curbs. A poured longi- 
tudinal expansion joint may become obstructed by pebbles or brick 
spalls dropping into the space or by the sand cushion's running into 
it, before the mastic is poured. The crown of the pavement may be 
lifted also by the expansion of freezing water in the soil behind the 
curbs. 

An upheaval may occur in a level stretch of pavement due to 
defective grouting. If only the top of the transverse joints are 
filled, the pressure of the expansion is concentrated at the top of 
the joints; and if the joints over a considerable area are in like con- 
dition, they may all fail at once — usually with a loud report and a 
general upheaval of the affected area. 

1061. Re-laying Pavement. If a brick pavement is to be main- 
tained in a fair condition, it will frequently be necessary to re-lay 
the pavement over patches and also over openings made to lay or 
repair sewers, water or gas pipes, electric conduits, etc., for with the 
utmost care and foresight many such openings will be made (§ 656- 
57) . The typical case is re-laying a pavement over a trench. 

In making the cut in the pavement alternate brick will some- 
times be broken in the middle, thus leaving three bricks with their 
ends in line, which would prevent a good bond of the new pavement 
with the old; and therefore these broken bricks must be " toothed 
out " so that only whole brick remain. This may be done by hand 
with a stout long-handled chisel and hammer, or with the pneu- 
matic chisel (Fig. 202, page 556). After the broken brick are 
" toothed out," the cut will have the general appearance shown in 
Fig. 204. Next the joint-filler should be chiseled off from the brick 
that are " toothed out," care being taken not to break the bond of 
these bricks with those adjoining. 

Before re-laying the concrete foundation, the soil in the trench 
should be thoroughly compacted; and particularly the soil that has 
run out into the trench from under the edge of the foundation, should 



AKT. 3] 



MAINTENANCE 



559 



be replaced and rammed laterally to give a firm bearing. The con- 
crete should then be laid and tamped as in the original construction. 
If the bedding course is sand, great care is necessary in packing or 
ramming it under the edge of the undisturbed pavement. 

As far as they are available, the old brick should be cleaned and 
used, for they will match the others in size and color. If new 
brick are used, they should be of exactly the same width as the old 




Fig. 204. — Patch Properly Toothed Out. 



ones so that the courses will match. The brick should be bedded 
in the sand or mortar bed-course so their upper faces conform to the 
surface of the pavement; and then the joints should be filled. If 
grout is used, two or three applications should be added as described 
in § 999-1004 ; and after the grout has taken an initial set, the patch 
should be covered with sand or straw which is kept wet for 3 or 4 
days. In this connection, see the latter portion of the second para- 
graph of § 1054. 

With care in making a re-placement, the patch can be made so 
that the original surface and strength of the pavement is fully re- 
stored; and if the work is well done, the patch will hardly be visible. 
Fig. 205, page 560, shows such a patch over a trench in a pavement 
in Cleveland, Ohio. This patch is visible only because of the differ- 



560 



BRICK PAVEMENTS 



[chap. XVII 



ence in color of the old and the new brick. In that city are many 
such repairs which are scarcely visible. 

Part of the reasons for this good work is that the back-filling of 
the trench is inspected and the pavement is re-laid by employees of 
the division of street repairs. 

1062. Cracks. The only cracks requiring consideration are lon- 
gitudinal ones, which are usually near the center of the road. The 
transverse cracks are usually narrower, and are less harmful. A 





Fig. 205. — Brick Pavement Re-laid over a Trench. 



longitudinal crack is likely to develop into a rut. A longitudinal 
crack may be due to any one of several causes. 1. It may be due 
to the heaving action of frost under the edges of the foundation. 2. 
It may be due to the settlement of the edges of the foundation when 
the frost is out under the edges of the foundation and not under the 
center. 3. It may be due to the shrinkage of the soil under the 
edge of the foundation due to the soil's drying out. 4. It may be due 
to expansion as explained in the last two paragraphs of § 1060. 

It is sometimes impossible to explain the cause of such cracks. 
They seem to be more common in the North than in the South; 
and hence it is concluded that frost is a common cause. They seem 



ART. 3] MAINTENANCE 561 

to be less frequent the flatter the crown of the pavement; and they 
seem to be less frequent with a flat than with a crowned subgrade. 

The only practicable thing that can be done with a longitudinal 
crack is to clean and fill it with a bituminous cement as described for 
concrete roads — see § 482. 

1063. Re- Surfacing. Re-surfacing is a method of radical repairs. 
There are many sand-filled pavements so badly worn and so full of 
depressions as to be of but little value as a pavement, which may 
be used as a foundation for a new wearing surface. There are three 
methods that may be employed in re-surfacing such pavements, 
viz.: (1) covering the brick with a bituminous surface; (2) turning 
the brick upside down and re-laying them; and (3) laying a new 
monolithic surface on the old pavement. 

The bituminous surface may consist of either asphalt or tar. 

1064. Asphalt Top. The asphaltic surface may be either asphalt 
concrete or a binder course and a Wearing coat similar to that of a 
sheet asphalt pavement. When the work is well done in every par- 
ticular, the result is very satisfactory; but there have been many 
failures, probably owing to the failure to meet one or more of the 
conditions necessary for success. There are several essential con- 
ditions to be fulfilled. 1. The original pavement must be absolutely 
rigid, and not show any vibration or settlement when a heavy load 
goes over it. The lack of rigidity in the original pavement or in 
portions of it which are re-laid preparatory to re-surfacing it, is one 
of the most common causes of failure of a bituminous top. 2. 
The surface of the old pavement must be leveled up by filling the 
depressions with concrete, so that the asphalt will be of nearly uni- 
form thickness, as otherwise it will creep and loosen from the brick. 
Depressions deeper than 2 inches should be filled with hydrauHc 
concrete; but depressions less than 2 inches deep may be filled with 
the mixture for the asphalt binder course (§ 812-24). 3. The asphalt 
must be of good quality and proper consistency. 4. The pavement 
must be perfectly clean. The dirt must not only be removed from 
the surface but also from the cracks for at least J an inch. This 
can be done with wire brooms, but it requires great care. The dirt 
can be removed more effectively with a fire hose than by sweeping. 

5. The brick should be perfectly dry when the asphalt is applied. 

6. The old brick should not be cold when the asphalt is applied. If 
a surface heater (Fig. 161, page 450) is available, it is wise to warm 
the old brick before applying the asphalt. 7. Apply a paint course 
of asphaltic cement thinned with naphtha, at the rate of not more 



562 BRICK PAVEMENTS [cHAP. XVII 

than a gallon to the square yard. Dust or dampness or cold will 
prevent the paint coat from adhering perfectly. 8. As soon as the 
naphtha has fully evaporated from the paint coat, and while it is 
still perfectly clean, the sheet asphalt should be laid and rolled. 

The sheet asphalt may be either a binder course and a wearing 
coat of a total thickness of 2 inches, or a wearing coat alone having a 
thickness of 2 inches. The binder course and also the wearing coat 
are to be mixed and laid as described for the corresponding opera- 
tions for a sheet asphalt pavement (§ 812-24 and § 825-45, respec- 
tively). Experience has shown that if it is possible, the asphalt 
surface should not be less than 2 inches thick at any point, as it is 
likely to creep and form humps. This is due to the fact that in rolling 
the binder course or the wearing coat, the wide roller will be sup- 
ported on the high points and not compress the asphalt in the holes; 
and later narrow tires will compress the asphalt in the holes and 
make a depression, and wheels dropping into these depressions will 
displace the asphalt and loosen it from the bricks. 

1065. One of the most difficult questions encountered in plan- 
ning to add a new surface to an old pavement is the matter of drain- 
age. The curb or gutter that was only deep enough for the original 
pavement will be too shallow if a new 2- or 3-inch surface is put on 
top of the old. This difficulty is not as serious on streets having 
considerable longitudinal grade as on nearly level streets. On the 
latter, either of two things may be done,* viz.: 1. Take up the old 
brick and the foundation next to the curb (or next to the combined 
curb and gutter) for a width of 3 or 4 feet, and lay a new concrete 
foundation at such a height that when the old brick are re-laid and 
the asphalt is placed thereon, the gutter will be of suitable depth 
(or the top of the asphalt will be even with the top of the concrete 
gutter). 2. Take up the old brick for 3 or 4 feet next to the curb 
(or next to the combined curb and gutter) and lay concrete in this 
space making its upper surface next to the gutter of such a height 
that the asphalt when laid thereon will given sufficient depth of 
gutter (or will come even with the top of the concrete gutter), and 
making the top of its edge next to the undisturbed brick level with 
the top of the brick. Of course, both of these methods increase the 
transverse slope of the pavement near the curb, but usually this is 
not serious. 

At street intersections that are not to receive an asphalt top, a 

* Thomas H. Brannan, Superintendent Asphalt Streets, Columbus, Ohio, in Proc. Amer. 
Soc. Municip. Improvements, 1916, p. 107-8. 



i« 



ART. 3] MAINTENANCE 563 

somewhat similar adjustment is necessary where the new asphalt 
top meets the pavement of the side street. 

1066. Tar Top. Tar has not been used for this purpose as much 
as asphalt, but it has been employed enough to show that it can be 
made to give reasonably satisfactory results. The method of apply- 
ing the tar is as follows: 1. The brick surface should be rigid, clean, 
dry, and warm as described in items 1, 4, 5, and 6 of § 1064. 2. 
All depressions more than 1 inch deep should be filled with hydraulic 
concrete. 3. All depressions less than 1 inch deep should be thor- 
oughly painted with tar, and then be filled with J- to |-inch broken 
stone perfectly free from dust. 4. The tar is then applied sub- 
stantially as described for bituminous carpets (§ 591-93), except that 
a greater quantity is applied, depending upon the degree the bricks 
are worn. Enough should be applied to have a layer of about | of 
an inch thick on the face of the brick. The tar should be well 
brushed or rubbed into the joints with a wire broom. 5. As soon 
as the tar is rubbed into the joints, a half -inch layer of stone chips 
is applied as described in § 594-95. 

When the surface is finished, it will have the appearance of a 
bithulithic pavement (§ 893), and will give good service for several 
years, depending upon the character and amount of traffic. When 
worn through, the surface can be renewed by the addition of a new 
coat of tar and screenings. 

Water injures a tar surface, and hence this treatment is more 
permanent the better the drainage of the surface. 

1067. Turning the Bricks. In„Ghampaign, Illinois, in 1916, two 
experiments were tried of laying a monolithic brick pavement on the 
existing concrete base, turning and using the old bricks. The old 
pavement was laid on a 2-inch sand cushion, and the joints were 
filled with sand. The brick were badly worn. 

The repair work was carried out as follows: 1. The concrete base 
was cleaned, and on it was laid a 2-inch layer of 1 : 3 : 2 gravel con- 
crete for a bedding course. 2. The brick were thoroughly cleaned 
with wire brushes, and laid on the bedding course before the con- 
crete had set. 3. The brick were rolled and grouted in the usual 
way (§991 and §996-1002). 4. The street was barricaded for 15 
days. 

In one section, the brick were very badly worn, and varied in 
depth from 2i to 4 inches. About 10 per cent had to be replaced 
with new ones. No attempt was made to size them, and it was 
difficult to get a smooth surface. If the brick had been sorted, and 



564 BRICK PAVEMENTS [CHAP. XVII 

the most worn ones placed next to the curb and the least worn at the 
crown, it is beheved a better surface would have been obtained with 
less labor. On the other section, the brick were not worn so much, 
and a good surface was obtained with much less trouble. The sur- 
face of this section compares favorably with that of a new mono- 
lithic pavement. The cost was 80 cents per square yard, which 
could doubtless be reduced with greater experience. 

1068. Monolithic Brick Top. In 1917 near Danville, 111., a 
new method of re-surfacing an old brick pavement was tried.* The 
pavement was on a suburban road which carries a dense and heavy 
traffic; and after considering asphalt, tar, and concrete as materials 
for the new surface, a monolithic brick surface with a thin concrete 
base was adopted. The concrete was one part of cement to four 
parts of fine, well-graded gravel; and its thickness varied from 1 to 5 
inches according to the depth of the holes in the old pavement. Part 
of the new brick were 4 and part 3 inches deep. The concrete, 
the bedding course, and the brick were laid as described under mono- 
Hthic pavements (§ 969, § 982, and § 996-1002, respectively). Fig. 
206 shows two views of this work in progress. The cost was $1.65 
per square yard; and the saving was substantially the cost of a 
new concrete base. 




Fig. 206. — Putting a Brick Top on an Old Brick Road. 

Obviously this method of re-surfacing would be inapplicable to a 
city street, on account of the difficulty of maintaining proper drainage. 

1069. Cost of Maintenance. As stated in § 868, the City 
of Buffalo, N. Y., is noted for the completeness of its records of the 
cost of construction and maintenance of pavements. The following 
is a summary for the cost of maintenance of brick pavements for 

• s * Harlan H. Edwards, Engineering News-Record, Vol. 79 (1917), p. 830-32. 



ART. 3] MAINTENANCE 565 

1 __^ — ^_ 

the year ending June 30, 1916. Of the twenty brick pavements over 
twenty years old, two short streets have required no repairs; and 
the repairs on the other eighteen streets cost from 0.22 to 4.92 cents 
per square yard per year, all but six costing less than 0.85 cent per 
square yard per year. Of the fifty brick-paved streets from ten to 
twenty years old and out of guaranty, twenty have required no 
repairs; and the repairs on the other thirty have ranged from 0.04 
to 1.58 cents per square yard per year, only three of these costing 
more than an average of 1 cent per square yard per year.* The 
average cost of repairs during 1915-16 on 231,355 square yards was 
2.9 cents per square yard.f 

* Report of Dept. of Public Works— Bureau of Engineering, 1915-16, p. 481-511. 
ilbid., p. 7Q. 



CHAPTER XVIII 
STONE-BLOCK PAVEMENTS 

1073. Stone-block pavements rank third in area among the 
permanent pavements, being exceeded by sheet asphalt and brick 
— see the tabular statement on page 320. 

1074. Classification. The earhest pavements of ancient 
times consisted of irregular shaped blocks of stone more or less 
accurately fitted together. The form and size of the blocks have 
varied greatly from time to time, a fact which has given rise to 
different classes of pavements. A few of these will be briefly 
described. 

1075. Roman Roads. The Roman roads so frequently referred 
to by modern writers are the earhest examples of stone-block pave- 
ments. The details of construction varied somewhat, but as a 
rule they were about as follows : The foundation was laid in a trench 
about 3 feet deep, with no attempt at underdrainage. The base 
was formed of one or sometimes two courses of large flat stones 
laid in lime mortar, and was usually about 15 inches thick. Upon 
this was laid a 9-inch course of small fragments of stone imbedded 
in hme mortar, the intention of this course apparently being to bind 
together the tops of the large stones in the course below. Next 
was laid a 6-inch layer of concrete, apparently to make a smooth 
bed to receive the stones of the top course. The wearing surface 
consisted of closely-jointed, irregular-shaped stones, about 6 inches 
thick. The total thickness of the road was about 36 inches. In and 
near the cities, the top course was formed of irregular blocks of 
basalt, porphyry, or lava, which had a top area of 4 or 5 square feet 
and a thickness of 12 to 15 inches. These blocks were dressed 
and fitted together with extreme accuracy, and were imbedded 
in cement. These ancient pavements have aptly been described 
as " masonry walls laid on their sides." 

The Romans seem to have located their roads in straight lines, 

566 



CLASSIFICATION 



567 



running them toward prominent land-marks without much regard 
to the topography or to natural obstacles. They were wasteful of 
materials and labor, which, however, cost nothing but the lives 
of captives who were forced to build these roads for the armies of 
their captors. The results were roads which are remarkable chiefly 
for their cost, and which were inferior to modern pavements costing 
only one eighth to one quarter as much. The durability of these 
roads does not seem so remarkable when it is remembered that the 
traffic was light, and consisted mostly of footmen, unshod horses, 
and ox-carts having wooden wheels, and also that probably the 
surface of the road was kept covered with earth two or three inches 
deep. 

1076. Cobble-stone Pavement. A cobble-stone pavement con- 
sists of cobble stones or small bowlders placed side by side upon a 
bed of sand or upon the natural soil. The stones, usually somewhat 
kidney-shaped, are selected with some relation to size, set on end 
side by side in holes dug in the sand or unconsolidated native soil 
by a laying tool, one end of which serves as a scoop and the other as a 
hammer to settle the stones in place, and lastly sand or fine gravel 
is spread over the surface to fill the spaces between the stones. Fig. 
207 shows a transverse section of a cobble-stone pavement; and 
Fig. 208, page 568, shows the only tool used in laying it. 




Fig. 207. — Section of Cobble-stone Pavement. 



The earliest pavements in many of the older cities, both American 
and European, were of this type; and until about the beginning of 
this century on account of their comparatively low first cost were 



568 STONE-BLOCK PAVEMENTS [CHAP. XVIII 



quite common. In 1884, 93 per cent of all the pavements in 
Philadelphia were made of cobble stones; but in 1901 less than 6 per 

t 4 ia>^--^^^^ cent were of this kind. In 1902 Baltimore 

^^^^^^ had 321 miles of cobble-stone pavement, 
— more than any other city in the United 
States, — over 90 per cent of the pave- 
ments being cobble stones. In Septem- 
'■ ■' ber, 1901, New York City still had 229 

Fig. 208^Cobble.8tone j^-^^g ^f streets paved with cobble stones. 

Hammer. i i n 

but nearly all of them have been replaced 
with better pavements. Since the introduction of asphalt, brick, and 
bituminous pavements, and since the decrease in the cost of stone- 
block pavement by the introduction of improved methods of quarry- 
ing and manufacture, there is no excuse for the construction of 
cobble-stone pavements, and little excuse for their continuance. The 
construction of such pavements has been practically abandoned, and 
in some cities it has been prohibited by law — like theft and murder. 

1077. Rubble Paving. In some cities having no cobble stones 
but having comparatively plenty of even bedded sandstone or 
limestone, the streets were paved by laying rough rubble stones 
flatwise, the stones being 4 to 6 inches thick and having a top sur- 
face of 4 to 6 square feet. The irregular joints between the stones 
were filled with spalls. The blocks chipped on the edges, wore round 
on top, and got out of place, thus making an exceedingly rough 
pavement. 

1078. Belgian-block Pavement. This is a stone-block pave- 
ment made of blocks nearly cubical in form, from 5 to 7 inches on a 
side. For a time this form of pavement was very common in both 
Europe and America. The objections to the Belgian pavement are: 
1, On account of the size and form of the blocks, it is difficult to 
keep them in place; 2, the blocks are of such a form as to give a poor 
foothold to horses; and 3, there is always a considerable length of 
joints parallel to the line of travel, which causes ruts to form in the 
pavement. Belgian blocks have usually been laid with their sides 
perpendicular and parallel to the sides of the street; but if a square 
block is to be used, it should be laid in courses diagonal to the street, 
so that no joints shall be parallel to the fine of travel, a method which 
would add some extra expense. The Belgian block has been dis- 
carded in this country for the oblong block. 

1079. Oblong Block Pavement. At present practically the 
only stone paving-blocks employed are about 3J to 4J inches wide, 



ART. 1] THE STONE 569 

8 to 12 inches long, and nominally 4 or 5 inches deep. They are laid 
on a concrete base with their longest dimension perpendicular to 
the line of the street. This is the form of stone-block pavement 
that will be considered in detail in this chapter. 

1080. Durax Pavement. This form consists of granite cubes 
from 2| to 4 inches on a side. This form of pavement will be con- 
sidered only briefly — see § 1117. 

Art. 1. The Stone 

1081. As stone-block pavements are employed only where the 
travel is heavy, the material of which the blocks are made should 
be hard enough to resist the abrasive action of the travel, and tough 
enough to prevent being broken by the impact of loaded wheels. 
The hardest stones will not necessarily give the best results in the 
pavement, since a very hard stone usually wears smooth and becomes 
slippery, and the edges of the block chip off and the upper face 
becomes rounded, thus making the pavement very rough. A hard 
stone may be necessary under a heavy traffic; but under medium 
traffic a softer stone may give more satisfactory results. 

The stone could be tested to determine its strength and dura- 
bility much as paving bricks are tested, but it is not known that any 
such tests have been made. An examination of a stone as to its 
structure, the closeness of its grain, its homogeneity, etc., may 
assist in forming an opinion as to its value for use in a pavem^ent; 
but in the present state of our knowledge, a service test in the pave- 
ment is the only certain guide. 

Granite, trap, sandstone, and limestone have been used for 
paving blocks. 

Granite paving blocks are much the most common, and ordinarily 
the term granite-block pavement is employed as being synonymous 
with stone-block pavement. 

1082. Granite. This is a massive, unstratified, granular rock 
composed essentially of quartz and feldspar; but almost always 
containing other components, such as mica, hornblende, and tour- 
maline in varying proportions. The quartz and the feldspar are 
called essential ingredients, since their presence is necessary to 
form a granite; while the other constituents are called accessories, 
since they merely determine the variety of the granite. The term 
granite is popularly applied to any feldspathic granular rock, and 
includes gneiss, syenite, and porphyry, or any crystalline rock 



570 STONE-BLOCK PAVEMENTS [CHAP. XVHI 

whose uses are the same as granite. Gneiss is a rock of granitic 
composition that has a decided banding or parallel arrangement 
of its mineral constituents. Syenite is a granitic rock containing 
no quartz. Porphyry is popularly any fine-grained compact rock 
having large crystals scattered throughout its mass. 

Granite varies in texture from very fine and homogeneous to 
coarse porphyritic rocks in which the individual grains are an inch 
or more in length. The color may be red, dark mottled, light to 
dark gray, or almost black. The durabihty is closely related to the 
accessory minerals present; and although granite is popularly 
regarded as the hardest and most durable stone, there are some nota- 
ble exceptions. A quartoze granite, one in which quartz predom- 
inates, is too brittle for paving purposes; a feldspathic granite, one 
containing an excess of feldspar, is too easily decomposed; and a 
micaceous granite, one containing considerable mica in parallel 
laminas, is too easily split for use in paving blocks. Gneiss is usually 
too much stratified to make a good paving material. Syenite is 
one of the gest materials for paving blocks, and usually the darker 
the color the better the stone. 

The crushing strength of granite usually lies between 15,000 and 
20,000 lb. per square inch. It is customary to specify that the 
granite shall have a toughness of not less than 9 (§ 342), and a French 
coefficient of wear of not less than 11 (§ 343). 

A most important property possessed by all granitic rocks is 
that of splitting in three planes at right angles to each other, so 
that paving blocks may readily be formed with nearly plane faces 
and square corners. So far as discovered, this valuable property is 
possessed only by the granitic and trappean rocks. This property 
is called rift or cleavage, and was caused by pressure before the rock 
was consolidated. The fine-grained granites possess the most perfect 
rift, and it decreases as the size of the grains increase, so that a coarse- 
grained variety is likely to require considerable dressing to bring the 
face of the block to a plane surface. 

1083. Granite paving-blocks are produced in large quantities 
in Wisconsin, Maine, New Hampshire, Massachusetts, North Car- 
olina, Georgia, and Minnesota. The order in the above list is that 
of the number of blocks produced in 1916, the first two states pro- 
ducing more than all the others. In recent years the production of 
granite paving-blocks has greatly fallen off, apparently more than 
one half, probably owing to the substitution of asphalt and brick 
for stone blocks for paving purposes; but the quality has greatly 



ART. 1] THE STONE 571 

improved, partly in response to a demand for smoother block- 
pavements; and partly by using smaller blocks, which can be cut 
more accurately; and partly by abandoning the use of the hardest 
granites and using the softer and finer-grained varieties, which split 
more easily and regularly and make a better wearing surface.* 

1084. Trap. This is a popular term appUed to any dark- 
colored, massive, igneous rock. Owing to the difficulty of making 
them, trap is not much used for paving blocks. 

1085. Sandstone. Sandstones are rocks made up of grains of 
sand which are cemented together by siliceous, ferruginous, calca- 
reous, or argillaceous material. The texture of the stone varies 
according to the sizes of the sand grains, of which there are all gra- 
dations from those that are so fine as to be barely discernible to those 
that are very coarse. The hardness, strength, and durability of the 
stone is dependent upon the character of the cementing material. 
Only the harder and tougher sandstones, generally those in which the 
cementing material is siliceous, are used for paving. Sandstone 
paving-blocks are common in the Lake and Western cities. The 
principal quarries from which sandstone paving-blocks are obtained 
will be briefly described. 

1086. Medina Sandstone. This stone is found in the state of 
New York, extending from Oneida and Oswego counties on the 
east along the shores of Lake Ontario westerly to the Niagara river. 
It is generally a deep brownish red in color, though sometimes light 
and yellowish, and in a few localities gray. The stone is evenly 
bedded, and the beds are divided into blocks by systems of vertical 
joints, generally at right angles to each other, an arrangement which 
greatly facilitates the work of quarrying. It absorbs 2| to SJ per 
cent of water, but it is not materially affected by alternate freezing 
and thawing. : 

This stone is much used for paving in the Lake cities, where it 
is often preferred to granite, since it does not wear slippery. 

1087. Potsdam Sandstone. .This formation is worked at a 
number of places in the state of New York, the largest quarries being 
near Potsdam. That quarried at Potsdam is hard and compact, 
evenly grained, and reddish in color. It is largely used as a building 
stone and to a considerable extent for pavements. 

1088. Colorado Sandstone. In Boulder County, Colorado; are 
several deposits of sandstone that furnish stone for paving purposes. 

* For an interesting and elaborately illustrated article on the Manufacture of Granite Paving 
Blocks, see Engineering News, Yol 73 {1915), D. 376-81. 



572 STONE-BLOCK PAVEMENTS [CHAP. XVIII 

It splits easily, and breaks readily at right angles, so that it is formed 
into flagging, curb stones, and paving blocks without difficulty. 
It is hard and tough, and wears well in a pavement. It is never slip- 
pery; and after a little wear forms a smooth and pleasing pave- 
ment, very similar to one made of Medina stone. 

1089. Sioux Falls Quartzite. This is a metamorphic sandstone 
quarried at Sioux Falls, South Dakota. The stone is almost pure 
siUca with only enough iron oxide to give it color, which varies 
from Hght pink to jasper red. It is very close grained, and will 
take a poHsh almost Hke glass. It is said to be the hardest stone 
in this country. Its crushing strength is about 25,000 lb. per square 
inch. It possesses a remarkably good rift and grain, although 
not so perfect as that of granite. It is used considerably as a paving 
material, being shipped as far east as Chicago; but it wears smooth 
with a glassy surface. 

1090. Kettle River Sandstone. This is a fine-grained, light- 
pink sandstone, found in large quantities at Sandstone, Minn., 
about a hundred miles north of Minneapolis, which has been used 
for paving purposes in Wisconsin and Minnesota. The stone wears 
flat, does not polish, and approaches granite in its resistance to 
crushing. 

1091. Limestones. These differ greatly in structure, from a 
light friable variety highly charged with fossils to a hard compact 
rock denser and heavier than granite. The thin bedded varieties 
are easily broken into paving blocks. Although some varieties of 
limestone are very dense and strong, it wears unevenly when used as 
a paving material, and the blocks are speedily shivered by traffic 
and spUt by frost, owing to the fact that the lamination is vertical. 

Art. 2. Construction 

1093. Fig. 209 shows a transverse section of the better form of 
stone-block pavements. 

1094. Foundation. The method of preparing the subgrade 
has already been discussed — see Art. 1, Chapter XV. Formerly 
the foundation always consisted of a bed of sand upon the natural 
soil (§966), but at present it is nearly always a layer of concrete 
(Art. 2, Chapter XV). Stone-block paving is laid only on streets 
subject to heavy travel. 

1095. Bedding Course. On the concrete foundation must 
be spread some material to even up the surface of the concrete and 



ART. 2] 



CONSTRUCTION 



573 



to give a good bed for the blocks. The smoother the surface of the 
concrete and the less the variation in the depth of the blocks, the 
thinner can be the cushion coat. Sand has generally been used for 
the bedding course, but recently cement mortar has been employed 
tentatively. 




Fig. 209. — Section of Stone-block Pavement. 



1096. Sand Cushion. The sand should be fine, clean and dry. 
The finer the sand the better. It should contain no pebbles 
greater than J inch in diameter. The sand should be clean so as to 
compress uniformly; and it should be dry so it will not shrink away 
from the blocks in drying out (§ 1055). 

In spreading the sand cushion for brick pavements, great care is 
taken to secure a bed of uniform thickness and density (§ 972), so 
that when the pavement is rolled, the surface will be smooth; but 
stone-blocks are not as uniform in size as bricks, and hence they must 
be settled to place by ramming each individual block, and therefore 
it is not necessary to spread the sand for stone-blocks with as much 
care as for bricks. However, for the best results, it is wise to spread 
the sand with a shovel as uniformly as possible, and then rake it to 
loosen up any spots that have been consoHdated by throwing down 
a shovelful of sand and to level it off and secure a layer of uniform 
thickness and density. After the sand is leveled off it should not be 
stepped upon ; and in laying the. blocks the men should stand upon 
those already placed. However, these precautions are seldom taken; 
and usually the blocks are deposited on the sand cushion and the 
man who sets them stands upon the sand cushion while at work. 



574 STONE-BLOCK PAVEMENTS [cHAP. XVIII 

The thickness of the bed should vary with the accuracy of the 
dressing of the blocks. ' If the more .inaccurately dressed blocks 
(paragraph 1, § 1100) are employed, a depth of 2 inches may not be too 
much; but if the most accurately dressed blocks (paragraph 2, 
§ 1100) are used and if the top of the concrete bed is reasonably 
smooth, the sand cushion need not be more than 1 inch. The sand 
cushion should be no thicker than is necessary to give a good bed for 
the blocks. 

1097. For a statement of the objections to a sand cushion for 
brick pavements, see § 977-78. These objections apply with nearly 
equal force to stone-block pavements. 

1098. Mortar Bedding Course. In view of the success of the 
monolithic brick pavement, particularly for rural roads (§979-82), 
it has been proposed to lay granite blocks in a mortar bedding-course; 
but there has been only a little experience with this form of con- 
struction. The mortar bedding course could be a dry mixture of 
cement and sand (§ 979) on a concrete base partially set, or a coat 
of green mortar on a concrete base which has not taken initial set 
(§ 982). 

Some claim that with a monolithic stone-block pavement on 
city streets it would be too difficult to make openings to lay or repair 
pipes, conduits, etc.; but this might be an advantage, if such a 
pavement would cause greater care in laying the pipes in the begin- 
ning. ■ 

1099. The Blocks. The blocks should be made of sound and 
durable stone, free from seams, and should be of uniform hardness, 
since the paVement will wear unevenly if hard and soft blocks are 
laid together. For the appearance of the pavement, it is desirable 
that blocks of only one color be laid together." 

Fig. 210 shows four stages in the manufacture of modern 
granite paving-blocks. 

1100.' Dressing. The blocks should be split and dressed so as 
to have as nearly, as possible plane rectangular faces and square 
corners. The more regular the blocks the thinner the joints, and 
consequently the smoother and more durable the pavement. In a 
general way there may be said to be three standards in dressing stone 
paving-blocks. • 

1. Formerly the blocks were roughly dressed; and would lay 
vdth joints f to 1 inch wide or perhaps more, and would show de- 
pressions of 1 inch under a 3-foot straight edge laid parallel to the 
curb. The joints were filled with pea gravel and sand or tar. 



ART. 2] 



CONSTRUCTION 



575 



2. Recently there has been a demand for a less noisy and more 
sanitary pavement, and hence the blocks have been more accurately 
dressed, and the joiht's have been filled with bituminous cement and 
sand or portland-cenient\grout. In. this case the blocks are dressed 
to conform to specifications about as follows: " The blocks shall be 




Fig. 210. — Fouk Views of the Manufacture of Granite Paving-Blocks. 



approximately rectangular on top and sides, and uniform in width. 
They shall be so cut that the joints between individual blocks when 
laid shall average not more than f of an inch. The head of the block 
shall have no depression greater than i inch from a straight edge 
laid in any direction and parallel to the general surface of the block."* 
Fig. 211, page 576, shows the two types of pavements described 
above. 

* Specifications, Borough of Manhattan, New York City, 1917. 



576 STONE-BLOCK PAVEMENTS [CHAP. XVIII 

3. It is very difficult to meet the above specification even when 
the best spUtting granites are available, and it is practically impos- 
sible with the harder granites; and further, if the joints are filled 
with cement grout, there is little need to require joints as thin as 



fc 



Old style in foreground; new style in background: 
Fig. 211. — Old and New Types of Stone Block Pavements. 

I inch. Therefore some good authorities specify that the blocks shalli 
be dressed so as to lay side joints not more than f of an inch wide,^ 
end joints not more than J inch, and that the top shall not depart 
more than I of an inch from a true plane. • 

1101. Re-cutting. Formerly the blocks were made larger, especi-| 
ally deeper, than is now considered good practice; and besides the; 
blocks were not dressed as accurately as is the custom at present. ; 
Consequently there are many stone-block pavements, particularly in ; 
the older cities, that are very rough and composed of comparatively 
large blocks; and hence in recent years many of these old blocks 
have been taken up, re-cut, and re-laid. Different methods are 
employed in breaking the old blocks depending Upon their size. 
For example, blocks 12 X 8 X 4 inches may be broken into four 
new ones 6X4X4 inches. But blocks either much smaller or 
much larger receive different treatment. For example, with a 
smaller block, sometimes a new block is taken from the end, and two 
new ones are made from the remainder of the old block by dividing 
the depth; and for larger blocks sometimes four new blocks may be 
taken side by side successively from the end.* The blocks are 

* For a liberally illustrated account of the method of re-CUtting granite paving-blocks, see 
Engineering News, Vol. 73 (1915), p. 1020-23, 



ART. 2] CONSTRUCTION 577 

usually dressed to conform to the specifications in paragraph 2 or 3 
of § 1100. The depth of the re-cut or napped blocks is usually less 
than that of the old ones; and therefore the re-cut blocks generally 
make a greater area of pavement than the original ones, the excess 
sometimes being nearly 100 per cent. The cost of taking up and 
re-cutting ranges from | to f of the cost of new blocks.* 

1102. Size of Blocks. For an ideal pavement the blocks should 
be of one size; but if it were necessary to cut the blocks to exact 
dimension, the expense would be unreasonably great. It is con- 
sidered good practice to allow variations in length from 8 to 12 inches, 
in width from 3| to 4| inches, and in depth from 4| to 5i inches. 
It is customary to require that the blocks shall be sorted according 
to width, and be laid in courses of practically uniform width. 

The above specifications are for a block nominally 5 inches deep; 
but a few cities use blocks nominally 4 inches deep. When stone 
blocks were usually set in the native soil or in a thick sand cushion, 
it was customary to make the depth 7 or 8 inches; but when a con- 
crete foundation was introduced, the depth was generally reduced to 
5 inches. It is probable that with the more accurate cutting 
now customary, with a concrete base, a mortar cushion-coat 
and a grout joint-filler, a 4-inch granite block meeting the spe- 
cifications of § 1100 will be more durable than either a 5-inch block 
with a sand cushion and a gravel filler, or a 7- or 8-inch block with a 
thick sand foundation and a gravel filler. The reduction of a block 
in depth by wear under the heaviest travel is inappreciable, partic- 
ularly with a rigid filler. For information concerning the use of 
granite blocks less than 4 inches deep, see § 1117-18. 

1103. Measuring. Usually the contractor buys the blocks by 
the thousand, but gets paid for them by the square yard; and there- 
fore it is to his financial advantage to use as many large blocks as 
possible. Again, the man who sets the blocks is usually paid by the 
square yard; and therefore it is to his financial advantage to make 
the joints as wide as he may. It is very undesirable that it should 
be to the financial interests of the contractor and of the paver to 
secure a poor pavement, i. e., one having large blocks and wide 
joints. An excess in the width of the block is more important than 
in the length, since it is proportionally a larger matter, and also 
since it has a more important influence upon the quality of the pave- 

* For an account of the history of re-cutting granite paving-blocks with examples of the 
saving in a number of cases, see Proc. Amer. Soc. Municipal Improvements, 1914, p. 321-35, 
and p. 336-42. 



678 STONE-BLOCK 1»AVEMENTS [cHAP. XVII 1 

merit; and therefore special care should be taken to prevent either 
an excessive width of blocks or too thick side-joints. This precau- 
tion was more important formerly than at present, since then the 
joints were filled, or rather partially filled, with pebbles, and con- 
sequently wide joints were more destructive than now; but never- 
theless the principle is still worth considering. To identify as far 
as possible the interests of the contractor with those of the city, the 
following method of measuring a stone-block pavement has been 
proposed.* 

"The blocks must be substantially smooth and square on all their faces, and 
within the limits of the following dimensions: Not less than 3^ inches nor more 
than 4 1 inches wide across their upper and lower faces; not less than 7 nor 
more than 8 inches deep; and not less than 8 nor more than 14 inches long, except 
where shorter stones are necessary to fill out courses. 

"The sum to be paid per square yard shall be ascertained as follows: The 
number of blocks per square yard upon which the bid of the contractor is based 
shall be 22^. The actual average] number of blocks laid per square yard shall 
be determined as follows : The City Engineer shall from time to time, during the 
progress of the work, measure the width of 50 to 100 courses, and from this deduce 
the average width of a course. The average length of the blocks is hereby fixed 
for the purpose of computing the number of blocks laid per square yard, at 12| 
inches, t 

"For each block or fractional part thereof, that the average number laid per 
square yard shall exceed 22|, there shall be added to the contractor's bid per 
square yard an amount computed at the rate of 9| cents per block. For each 
block or fractional part thereof, that the average number laid per square yard 
shall fall short of 22 5, there shalli,be deducted from the contractor's bid per square 
yard an amount computed at the rate of 9| cents per block." 

According to this method, if the contractor uses narrow blocks 
and thin joints, the price per squard yard is proportionally increased; 
but if he uses thick blocks and wide joints, the price per yard is 
decreased. To meet the case in which a contractor should buy large 
blocks at a considerable reduction, it might be wise to make the 
amount per block to be deducted greater than that added. For 
convenience in applying the above method, a table is computed 
which gives in one column the width of 50 courses and in a second 
column the corresponding number of blocks per square yard. Of 
course, the number of blocks to a square yard would vary with the 
specified dimensions of the blocks and with the width of joints. 



* By Horace Andrews, City Engineer of Albany, N. Y., in 1890 in Engineering Record, Vol. 
21, p. 314 and 329; Vol. 25, p. 110-11. 

t This value was determined by measuring a number of blocks in pavements laid with blocks 
of the size stated above. 



ART. 2] CONSTRUCTION 579 

which latter would vary with the different kinds of stone and even 
with the same kind from different quarries, and could be deter- 
mined in any particular case only by measuring the combined width 
of a number of courses of blocks in the pavement. The normal or 
contract number of blocks per square yard should be stated according 
to the quality of work desired. 

Some cities buy the blocks and contract for laying them, a method 
which ehminates the interest of the contractor in using large blocks. 
In some cities it is the custom for the contractor to buy the blocks by 
the square yard in the pavement, in which case the contractor pays 
only for the blocks accepted, and has no financial interest in the size 
of the blocks or the thickness of the joints. In Great Britain it is 
customary to buy the blocks by weight, a method which eliminates 
any interest of the contractor in the size of the blocks. 

1104. Some cities require the blocks to be inspected and sorted 
to sizes before being piled on the street. The advantages of this 
are: (1) After being stacked upon the street it is nearly impossible 
to inspect them, since only the outside blocks of the pile can be 
seen ; (2) when the blocks are being laid, the inspector has enough 
to do to watch the quality of the workmanship without having also 
to inspect the blocks; (3) removing rejected blocks from the pave- 
ment delays the opening of the street ; and (4) if the blocks are sorted 
before being piled upon the street, different sizes are not so likely 
to get into the same course, and therefore the joints will be narrower. 

In Cleveland, Ohio, where the specified width of the stone paving- 
block was from 3J to 5 inches, the blocks were sorted into three 
classes. Class No. 1 included blocks from 3i to 3J inches, Class 
No. 2 blocks from 3f to 4i inches, and Class No. 3 blocks from 4J 
to 5 inches. Blocks in Class No. 1 were marked with red paint, 
blocks in Class No. 2 with blue paint, and those in Class No. 3 with 
black paint, so that when the blocks were delivered on the street 
each class could be easily recognized and laid by itself. 

1105. Setting the Blocks. In placing the blocks, the work- 
man should stand upon the finished work, that the sand cushion 
may not be disturbed; but he usually 
stands on the sand cushion, the blocks 
being piled on the sand bed behind him. 
The workman with the pointed end of 
the hammer shown in Fig. 212 excavates ^'^- 212.-Stone Paver-s Hammer. 
a hole, if need be, into which to set the block. 

To secure the proper form to the surface of the pavement, a 




580 STONE-BLOCK PAVEMENTS [cHAP. XVIII 

chalk line is made upon each curb or a string is stretched in each 
gutter to indicate the top of the blocks, and a row of blocks 20 to 25 
feet apart is set in the center of the street with their tops to grade 
as determined by measuring down from a string stretched from 
curb to curb. If the street is wide, one or more rows of blocks 
are placed between the curb and the crown. Ordinarily the sur- 
face of the pavement is brought to grade between the guide blocks 
with the unaided eye; but in the best work, a straight edge or string 
is placed parallel to the line of the street on the guide blocks, by which 
to grade the surface, and between these Hues the blocks are brought 
to the surface indicated by a straight edge parallel to the line of 
the street resting upon the pavement already completed. 

The blocks should be set with their long dimension across the 
street, except at street intersections ; and should be placed in straight 
rows with as close joints as possible. Each course should be formed 
of blocks of uniform width and depth; and the bond should be ap- 
proximately half the length of a blocks or at least 3 inches. As the 
blocks are of uneven lengths, the securing of the proper bond requires 
careful attention. The paver is instructed to secure thin joints, and 
consequently has a tendency to set the block with the larger end up; 
but when set in this way the block will surely sink under traffic. 
Placing the large end of the block down makes a wide joint, which is 
objectionable if the joints are to be filled only with sand and pebbles 
(§ 1108), but is no serious objection if the joints are to be filled with 
hydraulic-cement grout (see § 1112). 

The courses at street intersections are arranged substantially 
as in brick pavem.ents (§ 988). The work should progress up grade 
and from the gutter towards the crown, so that the blocks may have 
no tendency to settle away from each other and thus increase the 
width of the joints. 

Fig. 213 shows four views of the laying of stone-block paving. 

1106. Ramming the Blocks. After the blocks have been 
placed, they should be thoroughly rammed until they come to a 
firm bearing. As a rule the workman is more interested in secur- 
ing a uniform surface than in bringing the blocks to an unyielding 
bearing. Each block should receive at least three hard blows — 
one near each end and one in the middle. The rammer employed. 
Fig. 214, page 582, weighs from 50 to 90 lb., ordinarily 60 to 75 lb. 

If, after being rammed, a block does not conform to the general 
surface of the pavement, it should be lifted out, and sand should 
be added to the sand bed or extracted from it to bring the top of the 



ART. 2] 



CONSTRUCTION 



581 




582 



STONE-BLOCK PAVEMENTS 



[chap. XVIII 




Fig. 214. — Stone-block 
Rammer.' 



block to the proper elevation. Any imperfect or broken blocks 
should be removed and be replaced with perfect ones. Finally 

each block should be adjusted so that it 
stands perpendicular to the sand bed and 
has its top face conforming to the surface 
of the pavement. The quality of the pave- 
ment depends largely upon the care with 
which this adjustment is made. 

The ranaming is likely to be slighted 
unless closely watched. The man who does 
the ramming is likely to tap lightly a block 
which if thoroughly rammed would be 
driven below the general surface of the 
pavement; and subsequent travel will force 
the stone down and make a depression in 
the surface. The important thing is to 
haye each block equally and sufficiently 
rammed., to bring it to a solid bearing on 
' the bedding course and at the same time 
bririg.its top to the proper elevation. 
To secure a thorough ramming of the pavement, it is sometimes 
specified that there shall begone rammer to each paver, and occa- 
sionally one rammer to two pavers. No ramming should be allowed 
within 20 or 25 feet of the course last laid, to prevent the tipping 
of the block out of the vertical position ; but all the blocks set should 
be rammed before work ceases for the day. 

Fig. 215 is a near view of a granite-block pavement. 

1107. Filling the Joints. Four materials are in common use 
for filling the joints of stone-block pavements, viz.: (1) pea gravel, 
(2) tar and sand, (3) asphalt and sand, and (4) cement grout. The 
first is used with joints that are | to 1 inch wide, and the others with 
joints f to f of an inch wide. 

1108. Pea Gravel. Where the joints are J to 1 inch wide, it is 
customary to fill them with pea gravel or pea gravel and tar. It 
is usually specified that the pea gravel shall pass a J-inch mesh and 
be retained on a J-inch mesh. If tar is to be poured upon the peb- 
bles, they should not be too small, or they will not permit the tar 
to flow freely to the bottom of the joint. Since the joints are wide 
and the blocks are roughly cut, the joints are usually partly filled 
(say, 1| to 2 inches deep) with pebbles before the blocks are rammed, 
to keep them in place during ramming. After the joints have been 



ART. 2] 



CONSTRUCTION 



583 



partially filled and the blocks have been rammed, the pebbles in the 
joints are tamped with a bar having a chisel-shaped end. The joints 
are next swept full of hot pebbles and again tamped. 

1109. There are two methods in more or less common use for 
completing the filhng of the joints. 

1. The fining is completed by spreading fine sand over the pave- 
ment to a depth of | to 1 inch, and allowing travel to work it into the 



"^ 



' ^.^«»— ^-^^._ 



^.■-,/ 




} ~ 4 




Joints in foreground not filled; joints in background filled with tar. 
Fig. 215. — Near View of Granite-block Paving. 



joints. Until recently this was the only method employed, and even 
yet it is quite common. When filled in this way, the joints are not 
impervious; and the filling does not aid much in keeping the blocks 
in position. 

2. Recently it has become the custom with the better class of 
stone-block paving to complete the filling of the joints by pouring 
hot tar over the pebbles. The tar is applied in substantially the 
same way as in the case of brick pavements — see § 1011-12. The 



584 STONE-BLOCK PAVEMENTS fCHAP. XVIlI 



pebbles should be perfectly dry, for an almost inappreciable amount 
of water will cause the tar to foam and will prevent it from adhering 
to the pebbles and from forming a water-tight joint. It may be 
necessary to dry the pebbles artificially. The tar must not be 
appHed when the pebbles are very cold. The joints should be 
entirely filled with the tar, to secure which it is usually necessary 
to pour the joints twice. To keep the contractor from having a 
financial interest in not filling the joints entirely full, it is sometimes 
specified that there shall be brought upon the ground not less 
than a stated number of gallons of paving cement for each square 
yard of pavement, and that whatever remains after the completion 
of the work is the property of the city. 

In some cases it is specified that the pebbles and tar shall be 
applied alternately in three stages. 

The quantity of tar required to fill the joints varies from 1 to 3 J 
gallons per square yard, according to the width of the joints, which 
varies with the quality of the stone and the workmanship. 

The tar in the joints makes the pavement impervious, and 
therefore more sanitary. The tar also assists in keeping the blocks 
in position, and therefore adds to the durabihty and smoothness of 
the pavement. 

Fig. 216 shows the process of filling the joints of a stone-block 
pavement with tar. Incidentally this figure also shows the differ- 
ence between the new and old types of pavements. 

1110. Tar and Sand. When the joints are nominally | of an inch 
wide, they are often filled with tar and sand, which is sometimes called 
tar-pitch mastic or pitch-sand mastic. The following are the speci- 
fications for this form of joint filler adopted by the American Society 
of Municipal Improvements.* 

"The joint filler shall be the paving pitch hereafter described [see § 576-77], 
thoroughly mixed with as much hot dry sand as the pitch will carry; but in no 
case shall the volume of the sand exceed the volume of the pitch. The sand shall 
be fine and clean, and all of it shall pass a 20-mesh screen. It shall be heated to a 
temperature of not less than 300 nor more than 400° F.; and shall be between 
these limits when mixed with the paving pitch. 

"The paving pitch shall be heated in kettles properly equipped with an 
approved thermometer, which shall register the temperature of the pitch. 

" The mixture shall be flushed on the surface of the blocks and pushed into 
the joints with suitable tools, re-flushmg or re-pouring, if necessary, imtil the 
joints remain permanently filled flush vnth the surface of the pavement. As 
little as possible of the mixture shall be left on the surface. 

♦Specifications for Stone-block Paving, as revised in 1916. 



I 



ART. 2] 



CONSTRUCTION 



585 



"In applying the filler care should be taken that the pavers are closely followed 
by the filler gang, and in no case shall the paving be left over night, or when work 
is stopped, without the filHng of the joints being completed. In case rain stops 
the filler gang before its work is finished, the joints should be protected by the 
use of tarpaulins or other means, to keep out water. Under no circumstances 
shall the filler be poured into wet joints." 

The tar pitch should comply with the specifications in § 576-77, 
except that northern cities, or rather cities that are subject to cool 




Modern pavement in foreground; old-style pavement in backgroimd. 
Fig. 216. — Filling the Joints with Tar. 



weather the greater part of the year, should use pitch having a melting 
point from 115 to 125° F., and cities which have long-continued hot 
weather should specify a melting point from 125 to 135° F. 

1111. Asphalt and Sand. The following are the specifications 
for this form of filler adopted by the American Society of Municipal 
Improvements. * 

"The joint filler used shall be the asphalt cement hereafter described [see 
§ 544], thoroughly mixed with as much hot, dry sand as the cement will carry; 
but in no case shall the volume of the sand exceed the volume of the cement. 
The sand shall be fine and clean and all of it shall pass a 20-mesh screen. The 

* Specifications for Stone-block Paving, as revised in 1916. 



586 



STONE-BLOCK PAVEMENTS 



[chap. XVIII 



sand shall be heated to a temperature of not less than 300 nor more than 400° F.; 
and shall be between these limits when mixed with the asphalt cement. 

"The asphalt cement shall be heated in kettles properly equipped with an 
approved thermometer, which shall register the temperature of the cement. 

"The mixture shall be flushed on the surface of the blocks and pushed into 
the joints with suitable tools, re-flushing or re-pouring, if necessary, until the 
joints remain permanently filled flush with the surface of the pavement. As 
little as possible of the mixture shall be left on the surface." 

The specifications for the asphalt cement referred to above are 
given in § 544, page 282. 

1112. Cement Grout. To secure the smoothest and most durable 
stone-block pavement, the joints should be filled with portland- 
cement grout, which should be mixed and apphed as described in 




Fig. 217. — Granite-block Pavement Eight Years Old. 



§ 996-1005. However, since larger quantities are required for stone 
blocks than for bricks, it is usual to permit the grout to be mixed in a 
batch machine-mixer. 

Fig. 217 shows a grout-filled granite-block pavement at Lowell, 
Mass., eight years old. 

The portland-cement grout makes the joint impervious, holds the 



AET. 2] CONSTRUCTION 587 

blocks firmly in position, prevents the edges from chipping and the 
top face from wearing round, and adds materially to the smoothness 
and durability of the pavement. 

1113. Expansion Joints. If the joints are filled with port- 
land-cement grout, an expansion joint of f to 1 inch in width should 
be provided next to each curb, constructed as described in § 1017; 
and expansion joints should be provided around manhole covers, 
water boxes, etc., as described in § 1021. 

If the joints are filled with pebbles or bituminous cement, no 
longitudinal expansion joints are necessary. 

Transverse expansion joints should not be provided, as they are 
not needed and are a decided detriment (see § 1018-20). 

1114. PAVING Adjacent to Track. Fig. 218 shows the 
standard method employed by the Paving Commission of Baltimore 
in laying granite-block pavement next to street-car rails.* 

£d/fuminou3 f/7/er 
, , nr cement grxxjf ^„^ , cGranfre bfocks 

9" Rail r Mortar bed , — ^ t"3and, \ 



C7 n un I mur lur ucu^^ ^ ^^ <- '~^'~" < ^ ^ 

' ^=i r* -i _=^« ^ --1";. — •-•"r •^••.' * •• 0'- V..,.- .; if. •>••-.'. -7 






Fig. 218. — Granite-block Paving Adjacent to Track, Baltimore. 

Granite blocks are much used for paving the railway area, because 
of their durability. When granite blocks are laid in the narrow strip 
between the rail and some other form of paving, they should be laid 
as stretchers or as headers, i. e., without toothing. 

In Worcester, Mass., an expansion joint is constructed between 
the pavement on the track area and that on the remainder of the 
street. The joint extends through the wearing coat and the con- 
crete foundation. The joint in the block course is made by nailing 
a pre-moulded mastic strip (§ 1017) against the ends of the ties. The 
joint is to prevent the rumbling of the grout-filled pavement due to 
the passage of a street car; and is effective. f 

1115. Maximum Grade. Stone-block pavements are freely 
employed upon grades up to 10 per cent; and if the stone is a quality 
that does not wear smooth, they may be used upon grades up to 
15 per cent. 



*Engineering News, Vol. 73 (1915), p. 884. 
t/6id., News, Vol. 74 (1915), p. 398. 



588 



STONE-BLOCK PAVEMENTS 



[chap. XVIII 



It has been recommended that on steep grades to afford a good 
foothold for the horses, (1) the edges of the blocks be chamfered, (2) 
that the joints be comparatively wide, and (3) that the joints be filled 
to within about an inch of the top with cement mortar. It is not 
known that these expedients have ever been employed; but the 
probabilities are that wide joints would be equally as effective 
without chamfering the blocks, since the edges spall off soon when 
the joints are wide and are filled with either gravel or tar. Further, 
the accumulation of dirt in the wide joints would probably largely 
neutralize their effect. Fig. 219 shows another method that has 
been proposed, but it is not known that it has ever been tried. 

1116. Merits and Defects. The only merit claimed for 
stone-block, particularly granite-block, pavement is durability. 
The material of the blocks does not decay or wear entirely out. 
But if the joints are filled with gravel or a soft filler, the face of the 
blocks wear round; and if a thick sand cushion is used, some blocks 
settle more than others. The result is that such a pavement becomes 
excessively rough and noisy; and if the granite is hard, the pave- 
ment is sUppery. 




^^^^^^^^M 






Fig. 219. — Stone-block Pavement on Steep Grade. 



However, if the blocks are carefully dressed, are of nearly uniform 
size, and laid with thin joints; and if they are laid in a mortar bed- 
ding course and the joints are filled with portland-cement grout, the 
pavement is very durable and not specially noisy. A granite-block 
pavement is the form universally chosen where there are many 
heavily laden steel-tired wagons and trucks. 

1117. DURAX Pavement. This is a pavement made of cubes 
of granite placed upon a concrete foundation. In America and 
England it is known as durax pavement, and in Germany as klein- 
pflaster. This pavement has been used in Europe since about 1885, 
but the first in this country was laid in the Brooklyn Navy Yard in 
1913. Since then it has been laid in a number of American cities. 

The blocks are approximately cubes having faces 2| to 3| inches 
square. They are usually cut to lay approximately |-inch joints. 



ART. 2] 



CONSTRUCTION 



589 



The cubes are generally machine made, and can be turned out cheaper 
per square yard than large hand-made ones; but on the other hand, 
they are not usually as accurately cut as the best large blocks. How- 
ever, since the durax blocks are nominally cubical, they may be laid 
on any one of three sides, which gives a little advantage in fitting 
them into place. The blocks may be laid with any. form of bedding 
course (§ 1095-98), or with any joint filler (§ 1107-12); but appa- 
rently they are usually laid on a 1-inch sand cushion, and with 
asphalt filler. 

The blocks are not usually laid in straight course, but in concen- 
tric segments of circles, in what is sometimes called the oyster-shell 




Fig. 220. — Laying a Durax Pavement. 

pattern. Fig. 220 shows the process of laying a durax pavement; 
and Fig. 221, page 590, is a close view of such a pavement.* 

The advantages claimed for the segmental form of courses are: 
1. There are only a few joints parallel to the direction of travel, and 
hence the stones wear better than in the ordinary oblong block pave- 
ment. This would not be important, if a grout filler is used. 2. 
Since there are no continuous transverse joints, opposite wheels of a 
vehicle can not drop into a joint at the same time; and hence there is 
less jar and less wear on pavement and vehicle. This would not be 
an important advantage, if the joints are filled with portland-cement 
grout. 3. Since the courses need not be kept straight, the blocks 
can be turned so as to give the narrowest joints. This may be an 
advantage in placing some of the blocks; but it is a disadvantage in 



* Engineering News, Vol. 72 (1914), p. 529. 



590 



STONE-BLOCK PAVEMENTS 



[chap. XVIIi 



making closures between different segments. On the whole, the 
joints can not be as narrow as with large blocks equally accurately 
cut. 

1118. The first cost of the blocks for durax pavement is less per 
square yard than for an ordinary granite-block pavement; but the 
labor of laying is much greater, and the total cost of the small-cube 




Fig. 221. — Oyster-shell Pattern of Durax Pavement. 



pavement is more than that of the large-block pavement. The 
small cubes have been used to re-surface old macadam or other 
pavements. One advantage of the small cubes is that they may be 
made of the same thickness as a brick or asphalt or wood-block 
pavement, and hence a durax surface may replace the old one with- 
out disturbing the old foundation or changing the grade of the pave- 
ment. It is said that durax pavements are not now being laid 
in Europe to any considerable extent, and that the area of durax 
pavements in Europe is only about 3 per cent of that of oblong 
blocks. 



ART. 2] CONSTRUCTION 591 

1119. Cost. Price of Blocks. The following is the market 
quotation for stone paving-blocks for November 1, 1917.* 

New York City, Manhattan, standard granite $2.50sq. yd. 

other boroughs standard granite 2 .25 " 

other boroughs 5-inch granite 2 . 55 " 

Boston standard granite 2 . 55 " 

Chicago, ordinary dressing, standard granite 1 .80 " 

best dressing standard granite. 2.25 " 

St. Paul standard sandstone 1 .65 " 

Kansas City standard limestone 2 . 15 " 

The variation in price is partly due to the difference ni freight 
and in price of labor, but chiefly to the ease with which the available 
material may be dressed. For example, according to data published 
by the U. S. Geological Survey, the average price of granite paving 
blocks per thousand in 1916 varied from $32 in California and $33 in 
Georgia to $62 in Minnesota and $66 in Wisconsin, the first two 
having easily worked granites and the last two granites difficult to 
work. Ordinarily, to lay a square yard of pavement requires 28 to 
31 blocks. 

1120. Granite-block Pavement. New York. In New York City 
in 1917 the cost of standard granite-block pavement is as follows: 



Items. 



Cost 
per Sq. Yd. 

Concrete Base, 6 inches: materials and labor $1 . 10 

Sand Cushion, 1 inch : material and labor 07 

Wearing Coat: 

29 blocks at 9 cents on street 2.61 

labor laying 22 

Total for wearing coat $2 . 83 

Joint Filling : 2 gallons of bituminous filler, sand, and labor of applying . . 45 

Total cost to contractor, exclusive of administration, tools, etc., and 

grading . $4 . 45 

With a cement-grout filler in place of the bituminous filler, the 
cost is about 20 cents less, or $4.25 per square yard. With a cement- 
grout filler and a cement-mortar cushion, the. cost is 5 to 10 cents 
per square yard less or $4.35 to $4.40 per square yard. In the 
Borough of Manhattan with the improved block there specified 
and with the difference in working conditions' in that Borough, about 
40 cents per square yard should be added, making the total cost about 
$4.85 per square yard. 

^Engineering News-Record, Vol. 79 (1917), Construction News, p. 179, 



592 STONE-BLOCK PAVEMENTS [CHAP. XVIII 

1121. Chicago. The average cost to the contractor of laying 
specially dressed granite blocks (3J to 4 inches wide, 8 to 10 inches 
long, 5 inches deep, of which 28 to 31 lay a square yard) at Chicago 
in 1917, was about as follows:* 

Items. ^J^^\r^ 

per Sq. Yd. 

Concrete Base: Ginches: materials and labor $0.92 

Sand Cushion: 

2 inches of sand at S2.50 per cu. yd 13 

labor spreading .021 

Total cost sand cushion $ . 15| 

Wearing Coat: 

granite blocks f.o.b. Chicago $2.35 

hauling to street 13 

carrying to paver 06 

la>dng and ramming .19 

Total for wearing coat $2 . 73 

Filling Joints: 

paving gravel at $2.00 per cu. yd $ .13 

labor spreading 04 

tar at 9 cents per gallon 10 

labor applying 07 

Total for joint filler $ .34 

Total cost to contractor, exclusive of tools, administration, etc , 

and grading $4 . 14f 

Ordinary granite blocks cost 25 to 30 cents per square yard 
less than the special dressed blocks above, the cost of laying is 
8 cents per square yard less, and the total of the other items is sub- 
stantially as above, thus making the total cost of the ordinary granite- 
block pavement on concrete foundation about $3.75 per square yard. 

1122. Removing, Re-cutting, and Re-lajdng. / kiladelphia. The 
following data on the cost of removing, x^e-cutting, and re-laying 
granite-block pavement are from experience in Philadelphia, f 

Removing old blocks $0 . 035 per sq. 3 

Clipping the old blocks to ^-inch joints 50 " 

Piling and inspecting new blocks 07 '' 

Sand cushion 08 " 

Laying and grouting. . . . .- . .22 " 

Gravel for filling joints 04 " 

Cost of grout 09 " 

Total '. $1,035 " 

*By courtesy of W. L. Wccden, Field Secretary of Granite Block Producers Association. 
fW. H. Connell, Chief of Bureau of Highways (Streets), Philadelphia, in Engineering and 
Contracting, Vol. 40 (1913), p. 290. 



ART. 2] CONSTRUCTION 593 

1123. Schenectady. Table 65, page 594, shows the details of the cost 
of re-cutting and re-laying 2,578 square yards of granite blocks in 
Schenectady, N. Y. * The old blocks were 12 by 8 by 4 inches ; and the 
new ones 6 by 4 by 4 inches, and were laid on a new 4-inch green 
concrete base with a thin bedding course of 1 : 3 dry cement mortar. 
The joints were filled with a 1 : 2 portland cement grout. The day 
was 8 hours. The work was done without interrupting travel. 

1124. Durax. The following data are from experience in Louis- 
ville, Ky., in laying a small area of cubical granite blocks, f The 
blocks were 3J to 4 inches on a side, were made in North Caro- 
lina, cost $9.30 per ton f.o.b. Louisville, and were guaranteed to lay 
7 square yards per ton, and consequently the guaranteed price 
was $L33 per square yard, which was 67 cents per square yard less 
than standard-size blocks from the same quarry would have cost. 
A man laid 2.2 square yards per hour, whereas of standard blocks 
he would have laid 3.3 to 4 square yards per hour. 

1125. Medina Block. Buffalo. For somewhat obvious reasons, 
the prices in 1917 were quite erratic, and hence it is not wise to cite 
them. Table 66, page 595, shows the representative cost of a Medina- 
sandstone block pavement in Buffalo, N. Y., in 1916. { 

1126. Cleveland. Table 67, page 596, shows the representative 
cost of Medina-sandstone pavements in Cleveland, Ohio, under a 
5-year guarantee, in 1916. § 

1127. Rochester. Table 68, page 597, shows the cost of Medina- 
sandstone pavements at Rochester, N. Y., in 1917. 

1128. Cost of Grouting. 1 1 Lawrence. The cost at Lawrence, 
Mass., of grouting standard granite blocks was as follows: Cement 
cost $1.08 per barrel, pea gravel $2.30 per cubic yard, sand $1.00 
per cubic yard. To hold the blocks in place while being rammed, the 
joints were filled to a depth of 1 inch with pea gravel. The grout 
was mixed 1 : 1 in iron boxes (§ 997), and scooped onto the pavement 
and broomed. With wages at $2.25, the cost of applying the grout 
was 6.4 cents per square yard. The total cost of the grout in place 
was 26| cents per square yard. 

1129. Lowell. At Lowell, Mass., grouting granite blocks on a 

*Chas. A. Mullen, City Engineer, in Municipal Engineering, Vol. 46 (1914), p. 431. 

t D. R. Lyman, Chief Engineer of Department ot Engineering, in Engineering News, Vol. 72 
(1914), p. 948. 

t Frank L. Bapst, President German Rock Asphalt Co., which company lays much stone- 
block paving in Buffalo. 

§ Robert Hoffman, Commissioner and Chief Engineer, Department of Public Works, Cleve- 
land. O. 

II Engineering and Contracting, Vol. 44 (1915), p. 350-51. 



594 STONE-BLOCK PAVEMENTS [CHAP. XVIII 

TABLE 65 
Cost op Re-Cutting and Re-Layjng Granite-Block Pavement 

Schenectady, N. Y. 
Taking up old pavement and preparing subgrade: gq yd 

Labor removing asphalt surface and concrete base, at $2.25 per day. $0.0445 
Team " '' '' " " " $5.00 per day. .0156 

Labor removing old granite blocks at $2.25 per day 0305 

" regulating and preparing subgrade at $2.25 per day 0417 

Team hairiing materials from subgrade at $5.00 per day 0241 

Total $0. 1564 

Concrete Foundation — 1 : 3 : 6. 4 inches thick: 

Labor mixing and placing, at $2.25 per day $0. 1192 

Cement, delivered ($1.24 per bbl. f.o.b. cars) 1018 

Sand, " ($0.25 per ton f.o.b. bank) 0275 

Stone, " |-inch at $1.30 per ton f.o.b. track i 

li-inch at $1.75 per ton on job ) ^^^^ 

Total $0.3320 

Bedding Course — 1 : 3 cement mortar: 

Labor, mixing and placing, at $2.25 per day. $0.0738 

Cement, delivered ($1.24 per bbl. f.o.b. cars) 0868 

Sand, " (25 cents per ton f.o.b. bank) 0242 

Total $0. 1848 

Re-cutting and re-laying granite blocks: 

Labor breaking and dressing, at $5.00 per day $0. 7385 

" sharpening and making tools 0501 

Materials for sharpening and dressing tools 0058 

Horse and wagon, moving blocks at $4.00 per day . . 0059 

Labor transporting blocks to pavers at $2.25 per day 0396 

" setting blocks, at $5.00 per day 1796 

" ramming blocks, at $2.25 per day .0065 

Total $1.0260 

Grout Filler — 1 : 2 portland cement: 

Labor mixing and placing, at $2.25 $0.0466 

Cement, delivered ($1.24 per bbl. f.o.b. cars) 0707 

Sand, " (25 cts. per ton f.o.b. bank) .0106 

Total $0. 1279 

Over-head charges: 

Foreman at $4.00, assistant foreman at $3.50, etc $0.0819 

Watchman at $2.25. 0552 

Total $0.1371 

Extras: 

Repairs to curbs, sidewalks, sewers, etc $0 . 0430 

Total cost of removing, re-cutting and re-laying $2 . 0072 



ART. 2] CONSTRUCTION 595 

TABLE 66 
Cost of Medina-Block Pavement in Buffalo in 1916, 

Concrete Foundation, 1:8: 

cement at $2.00 per bbl, f.o.b. Buffalo $0.37 

sand I 22 

crushed stone f 

mixing and laying, at 37^ cents per hour .15 

Total for concrete base $0 . 84 

Sand Cushion: labor and material $0 . 15 

Wearing Coat: 

blocks f.o.b. quarry $1 . 60 

freight Medina to Buffalo 18 

unloading and hauling, at 75 cents per hour for team and driver 20 

labor laying blocks, at 60 cents per hour 35 

Total for wearing coat $2 . 33 

Filling Joints: 

cement at $2.00 per bbl, f.o.b. Buffalo $0.08 

labor applying grout 25 

Total for filling joints $0.33 

Miscellaneous: 

overhead expenses $0 . 10 

indemnity insurance at 3.17% of pay roll 025 

discount on City time warrants, 3% 11 

maintenance during 10-year guarantee period 10 

paid city for water 02 

Total miscellaneous ,$0 . 355 

Total cost of pavement exclusive of excavation $4 . 005 

2-inch sand cushion with 1 : 1 grout required 0.295 bag of cement per 
square yard; and the average cost was24| cents per square yard. 

1130. Worcester. At Worcester, Mass., a 1 : 1 grout required 
0.36 cubic foot of cement per square yard; and the total cost of 
grouting was 24 cents per square yard. 

1131. Albany. At Albany, N. Y., the cost of grouting standard 
granite blocks having side joints not exceeding J inch, using 1 : 1 
grout mixed by machine, cost 13.9 cents per square yard. The cost 
of mixing by machine was 1.5 cents per. square yard, and by hand 
5.25 cents per square yard. The cement required was 0.4 bag per 
square yard. 

1132. Philadelphia. At Philadelphia, Pa., when each standard 
block is " struck in " at the base to secure a close joint, and when 
2 inches of pea gravel are deposited in the joints before ramming, a 



596 STONE-BLOCK PAVEMENTS [CHAP. XVIII 

TABLE 67 

Cost of Medina-Block Pavement in Cleveland in 1916. 

Cost 
Items. per Sq. Yd. 

Concrete Base, 6 inches of 1 : 3 : 6: 
materials and labor* $0 . 98 

Slag Cushion, 2 inches: 

material and labor spreading 08 

Wearing Coat, 6 to 6^ inches thick: 

stone blocks, f .o.b. quarry 1 . 65 

freight Medina to Cleveland 54 

transporting from car to street, at 90 cents per hour for team 10 

laying 45 



Total for wearing coat $2 . 74 

Tar Filler: material and labor 35 

Foreman: supervision 02 



Net cost to contractor . $4.17 

Overhead: administration, depreciation, interest, profits, etc 78 

Price bid, exclusive of excavation $4 . 95 

Granite blocks cost $2.50 per square yard, f.o.b. cars Cleveland, which is 
31 cents per square yard more than Medina blocks. 

1 : IJ grout required 0.27 bag of cement per square yard. The total 
cost of grouting, using mixing boxes (§ 997) and including contractor's 
profits, was from 17 to 20 cents per square yard. 

1133. Cost of Tar-sand Filler. At Englewood, N. J., the total 
cost of applying a 1 : 1 tar-sand hand-mixed filler on standard 
blocks having J-inch joints in which had previously been deposited 
" a small amount of grit," was as follows :t 

Pitch, — 1.7 gallons per square yard $0. 143 per sq. yd. 

Labor handling the pitch 02 

Grit Oil 

Sand 019 

Labor 038 



Total $0,231 

" Investigation showed that in every case the filler penetrated 
to the bottom of the block. It was also found that the volume of tar 
required to fill the joints was less than that smeared over the surface 
of the pavement in the two or three successive pourings." 

* Sand $1.15 per ton f.o.b. cars Cleveland; broken stone $1.35 per ton f.o.b. cars. Loading 
and hauling sand and stone, 30 cents per ton per mile. Labor from 30 to 43 cents per hour, 
t Engineering and Contracting, Vol. 47 (1917), p. 134. 



ART. 3] MAINTENANCE 597 

TABLE 68 
Cost of Medina-Block Pavements in Rochester in 1917 * 

Cost 
Items. per Sq. Yd. 

Concrete, 6 inches: 

materials and labor $1 . 00 

Sand Cushion, 2 inches : 

sand at $1 . 50 per cu. yd. in place 09 

Wearing Course, 6 inches deep: 

blocks f .o.b. quarry 1 . 50 

freight to Rochester 07 

loading and unloading 03 

hauling 1 mile . 05 

distributing and sorting 03 

laying 15 

Filling Joints: 

0.025 cu. yd. sand at $1.50 .04 

1^ gallons of tar at 10 cents 23 

labor applying filler 09 

Superintendence : 

foreman at 40 cents per hour for 30 square yards 015 

Total cost to contractor exclusive of administration, tools, etc $3.29 

1134. Contract Price. Table 69, page 598, shows the contract 
price of stone-block pavements in various cities, and incidentally 
gives considerable detailed information as to the practice in the 
several cities. 

Art. 3. Maintenance 

1135. There are almost no data concerning either the method or 
the cost of maintaining granite-block pavements. Formerly, when 
the wide-joint and roughly dressed granite-block pavement was the 
only form, little or no attention was given to methods or cost of 
pavement maintenance, and this was particularly true of granite- 
block pavements. Since the introduction of the better dressed narrow- 
joint granite-blocks, there has not been time in which to develop a 
system of maintenance nor to determine the cost, particularly as a 
modern granite-block pavement is very durable and needs no repairs 
for the first few years. 

* By courtesy of Walter L. Weeden, Secretary Granite Paving Block Manufacturers' Asso- 
ciation. 



598 



STONE-BLOCK PAVEME.^TS 



[chap. XVIII 



TABLE 69 
Contract Price of Stone-block Pavements in Various Cities * 

Laid in 1912 



Locality. 


Amount 

Laid in 

1912, 

sq. yd. 


CoNCKETE Base. 


Kind 

of 
Filler. 


Guar- 
antee, 
years. 


Total 
Thick- 
ness, 
inches. 




State. 


City. 


Thick- 
ness, 
inches. 


Propor- 
tions. 


age 
Pricei 
sq. yd. 


California. . . . 


Oakland 

San Francisco 

Ansonia 

LaGrange. . . 

New Orleans . 

Portland. . . . 

Lawrence. . . . 
Leominster . . 

LoweU 

New Bedford. 
Westfield. . . . 

Duluth 

Minneapolis. . 

Kansas City. 

Newark 

Rochester. . . 
Troy 

Portland. . . . 

Scranton. . . . 
Wilkesbarre. . 

Seattle 

Tacoma 

Superior 

Montreal. . . . 

Ottawa 

Saskatoon . . . 
Vancouver. . . 


11 445 

21 565 

1 500 

5 000 
4 119 
1004 

30 704 

2 268 

22 418 

12 310 

6 197 

23 146" 

7 9004 

13 248 

75 735 

42 700 
4 000 

3 914 

1 688 

2 156 

17 436 
11 002 

10 078 

48 000 
10 041 
16 662 
55 359 


6 




grout 
gravel 





■ V'Jg 


$4 . 002 
3 502 


Connecticut. . . 


6 


1:3:6 


2 10 


Georgia 

Louisiana 


tar 

grout 

grout 

grout 
pitch 

grout 

grout 
grout 

grout 



3 


10 
14 


1 75 


6 


1:3:6 


3.95 
2 30 


Massachusetts 
Minnesota. . . . 


6 
4 
6 
4 
4 

5 


1:3:6 

1:3:5 

1:4:11 

Hassam 

1:3:6 

1:3:6 




4 

' i 

5 


1\ 

'\2" 
10 

8i 

13 


2.72 

2.47 

3.15 

1.902 

3.30 

2.68 2 
2 754 


Missouri 

New Jersey. . . 
New York. . . . 

Oregon 

Pennsylvania . 

Washington. . . 

Wisconsin .... 
Canada 


6 


1:3:6 


5 

5 

5 
5 

5 

5 

5 
5 
5 
5 


13 

13 

12 

9 
12 

12 

lU 

13 

12 
13 
11 
13 


3.10 
3 03 


6 
6 

6 


1:3:6 
1 : 5 

1:3:6 


grout 
grout 

grout 

sand 
grout 

grout 
grout 

grout 
grout 
grout 


3.18 
3.35 

3.45 

2 10 


6 

6 
6 

5 

6 
6 
5 

6 


1:2:5 

1:3:6 
1:3:6 

1:3:5 

1:3:6 
1:3:6 
1 -.Ih 
1 : 21 : 5 


2.70 

3.50 
2.50 

2.52 

3.65 
3.78 
5.10 
4.50 



1 Including grading and concrete base. 2 Not including grading. 
3 Part grout and part pitch and tar. ^ Kettle River Sandstone. 

1136. Repairs Required. The repairs ordinarily required 
are re-laying small areas, re-filling the joints, repairing spalling joints, 
raising low blocks, repairing where the foundation has settled, and re- 
laying over trenches or other openings. 

1137. Re-laying. At present the most common work required 
in connection with the maintenance of stone-block pavements is 
taking up the old blocks, re-cutting, and re-laying them, which is a re- 
construction rather than repair or maintenance; and usually the 
new pavement is of entirely a different type than the old. This 
subject has already been considered in § 1101. 

* Engineering and Contracting, Vol. 39 (1913), p. 378-79. 



ART. 3] MAINTENANCE 599 

1138. Re-filling Joints. If a bituminous filler is used, it may 
run out of the top of the joints, particularly near the crown, or be 
picked out by the traffic. When this occurs, the joints should be 
poured again. With dense traffic this may be required every two or 
three years. With a good portland-cement filler, the joints are not 
likely to need re-filling; but if it develops that in spots the filler was 
poor, the joints should be digged out and again filled. 

1139. Spalling Joints. If pea gravel or sand is put into the 
joints, there is danger that the grout filler will fill only the top of the 
joint; and hence that the pressure due to expansion of the pavement, 
being concentrated near the top of the joint, will cause the edge of the 
block to spall. Usually there will be no spalling, if the grout pene- 
trates 3 inches; but if the penetration is 1 inch or less, the blocks are 
likely to spall — generally the first summer after the pavement 
is completed, but sometimes not for two or three years, depending 
upon the time required for travel to fill the joints opened by the 
contraction of the pavement. 

The spalling at joints can be prevented by clearing the joints of 
sand or gravel to a depth of 3 inches before applying the grout filler. 
If spalling occurs in the finished pavement, the blocks should be 
taken up, the joints cleaned, the blocks re-laid, and the joints re- 
filled. 

In effect this is substantially the same defect as that of brick 
pavements described in § 1059. 

1140. Raising Low Blocks. If a block was not properly 
bedded or sufficiently rammed, it may become depressed under 
travel, particularly with a thick sand bedding-course; and if so, it 
should be taken up, and re-laid. If a grout filler is used, it is prac- 
tically impossible to remove a block without destroying it; and this 
is reason for special care in bedding and tamping blocks that are to 
be grouted. 

1141. Settlement of Foundation. If there is a depression on 
the surface, it may be due to a settlement of the foundation and 
can be corrected substantially as described for brick pavements, 
see § 1056. 

1142. Settlement of Trench. The effect and the remedy of 
the sinking of a stone-block pavement is the same as that of a 
brick pavement, see § 1057 and 1061. 

1143. Cost of Repairs. There are almost no data on the cost 
of repairs for stone-block pavements, probably partly because of their 
long life and partly because only few repairs are ever made, the pave- 



600 



STONE-BLOCK PAVEMENTS 



[chap. XVIII 



ments usually being allowed to continue in a bad state of repairs 
The only data on record seem to be cost of repairs in Buffalo, N. Y. 
(see § 868), where most of the stone-block pavements are Medina 
sandstone (§ 1086). In 1916 the annual cost of repairs on 218,090 
square yards was 3.66 cents per square yard.* 



♦Report of Dept. of Pub. Wks. — Bureau of Engineering, 1915-16, p. 70. 



CHAPTER XIX 
WOOD-BLOCK PAVEMENTS 

1144. Kinds of Pavements. There are two forms of wood- 
block pavements, viz. : the round-block and the rectangular-block. 

1145. Round-block Pavement. Fig. 222 shows the usual form 




Fig. 222. — Round Wood-block Pavement. 



of round wood-block pavement. This form is often called a cedar- 
block pavement, since the blocks are usually sections of cedar 
poles or trees. These blocks are generally placed on a foundation 
of planks nailed to scantling which are placed on, or rather in, 
sand. 

Until about the close of the last century, untreated round wood- 
block pavements were laid in considerable quantities in localities 
where lumber was cheap; but now they are seldom laid, owing chiefly 
to the rapid increase in price of lumber and partly to the introduction 
of other cheap forms of pavements. Such pavements are laid now 
only where first-cost is the controlling factor, as for example, in new 

601 



602 



WOOD-BLOCK PAVEMENTS 



[chap. XIX 



city additions in states where the first pavement is selected and paid 
for by the owners of the abutting property, and the cost of mainte- 
nance and renewal is paid from the general property tax. In view 
of these facts, the round wood-block pavement will not be further 
considered in this volume. 

1146. Rectangular-block Pavement. Fig. 223 shows the usual 




Fig. 223. — Rectangular Wood-block Pavements. 



form of rectangular wood-block pavement. The rectangular block 
is usually treated with a preservative when used for paving pur- 
poses. This type of pavement will be considered in detail in this 
chapter. 

1147. Historical. Wood appears to have been employed as a 
paving material first in Russia, where though rudely fashioned it 
has been used for some hundreds of years. Wood pavements were 
first laid in New York City in 1835-36, and in London in 1839. 

The first wood used for pavements was untreated (§ 1145). The 
first pavement in this country made of treated blocks was laid in 
Galveston, Texas, in 1874; and remained in service for 29 years. 
A treated wood-block pavement was laid in St. Louis, Missouri, in 
1882-85; and remained in use until worn out by the traffic. The 
first extensive use of treated blocks for pavements was in Indianap- 
olis in 1896; and after 21 years these blocks are still in use and are 
said to be in a good state of preservation. Although a number of 
methods of preserving timber piles, railroad ties, etc., had been used 
in this country for several years, it was not until about 1900 that 



ART. 1] MATERIALS AND TREATMENT 603 

there was any considerable use here of a preservative for wood 
paving-blocks. 

1148. In 1909 3i per cent of the pavements in the United States 
were wood-block (see table on page 320); but in 1900 such pave- 
ments constituted 10 per cent of the total (see a table similar to that 
on page 320, in the former edition of this volume). This seems to 
prove that the percentage of wood-block pavements is rapidly 
decreasing. However, the decrease is wholly in the untreated-block. 
The percentage of treated-block pavements is rapidly increasing, 
although it is still less than 1 per cent of the pavements included 
in the table on page 320. 

Art. 1. Materials and Treatment 

1150. The Timber. Both hard and soft woods have been em- 
ployed for making paving blocks. The hard woods were used 
untreated, and the' soft varieties were treated. At present only 
treated timber is used; and of course the softer and cheaper woods 
are preferred, since they only can be impregnated with the preserva- 
tive. Exceptions to the above statement are two Australian hard 
woods, jarrah and karri, that are much used in London without 
treatment. 

1151. Jarrah and Karri. Jarrah is short grained and free split- 
ting, and breaks with a clean fracture and burns with a black ash. 
In color it looks nearly like cherry. When seasoned, it has a specific 
gravity of 1.01 and absorbs about 10 per cent of water when im- 
mersed 48 hours.* Its transverse and crushing strength is about 
the same as that of English oak and Indian teak. 

Karri is interlocked in the grain and is difficult to split ; it splinters 
in breaking and burns with a white ash. It is a little lighter colored 
than cherry. When seasoned, it has a specific gravity of 1.12, and 
absorbs about 7 per cent of water when immersed 48 hours. Its 
transverse strength is a Uttle greater than that of English oak or 
Indian teak, and its crushing strength is considerably greater. 

For street paving, there is little difference between jarrah and 
karri, although for exceptionally heavy traffic karri shows slightly 
less wear. Karri shrinks less than jarrah. Both timbers are very 
plentiful in Western Australia, the trees growing with large, long 
straight bodies without Hmbs. Jarrah and karri are preferred in 
some vestries of London to any other form of wood paving-blocks. 

* Most soft -woods will absorb 20 to 25 per cent. 



604 WOOD-BLOCK PAVEMENTS [cHAP. XIX 

1152. Wood for Treated Blocks. The cost of lumber in the 
United States in the last few years, even before the Great European 
War, has been so great that the first cost of the blocks is an important 
consideration. Southern long-leaf yellow pine was almost exclusively 
used in early treated wood-block pavements; and is most largely 
used at the present time. It makes the most durable blocks of any 
timber yet tried. However, it is not entirely satisfactory, for the 
hardness which gives it durability against wear also makes it sHppery; 
and further, it is Uable to split when the blocks are taken up to 
repair underground work. Nevertheless, long-leaf yellow pine is the 
most satisfactory timber for treated wood-block pavements. How- 
ever, as this timber is produced in only one section of the country 
the transportation charges are Hkely to be high, and besides the 
supply is nearly exhausted; and therefore where traffic conditions will 
permit, it is desirable to use a cheaper material. 

Some years ago the U. S. Forestry Service, to obtain data as to 
the relative value of different species of wood for paving purposes, 
laid a great variety of woods under the same conditions on a street in 
Baltimore, Maryland, and conducted a similar experiment in Minne- 
apolis, Minnesota. The conclusion reached as a result of the exami- 
nation of the Baltimore experiment after four years of service, \^£s 
that the different varieties could be grouped into classes in the order 
of the value for paving purposes as follows: (1) Southern long-leaf 
yellow pine; (2) Norway pine, white birch, tamarack, eastern hem- 
lock; (3) Western larch; and (4) Douglas fir. The conclusion from 
the Minneapolis experiment after eight years of service was sub- 
stantially the same. 

The 1917 specifications of the American Wood Preservers' Asso- 
ciation and also those of the American Society of Municipal Improve- 
ments call for Southern pine, which permits the use of either long- 
leaf or short-leaf Southern pine. 

1153. Specifications for Blocks. Dimensions. The width was 
formerly 4 inches; but in recent practice it is sometimes 3 inches. 
The length varies widely so as to make available planks of different 
widths. The length specified is usually 5 or 6 inches to 10 inches; 
and often the average width is specified to prevent the use of too 
many short or too many long blocks. The average length is usually 
6 or 8 inches. The depiti must be enough to give the block stability, — 
say, 3 inches. This depth is used where the traffic is light; but 
under heavy traffic the depth is 4 inches, and in extreme cases 4i 
inches, as for pavements in the Borough of Manhattan, New York 



ART. 1] MATERIALS AND TREATMENT 605 

City. If a 3-inch block is used its length should not exceed 
8 inches. 

While it is usual to specify that all the blocks for one job, or at 
least in any one city block, shall be of the same width, it is customary 
to permit a variation of | inch in the width. A variation of re i^^ch 
in depth is generally permitted. Sometimes, to prevent a block from 
being laid on its side, it is specified that there shall be a difference 
between the width and depth of at least | inch. 

1154. Quality of Blocks. The blocks should be sawed square and 
true. They should be free from large, unsound, loose, or hollow 
knots; and should not contain any shakes, checks, or other defects. 
The blocks should be free from any blue tinge, which is a sign of 
incipient decay. 

Specifications usually state the minimum number of annual rings 
permitted — some permitting 5 or 6 per hnear inch, and others not 
less than 8 or 9. The amount of sap wood allowed varies from 10 to 
40 per cent. In the early use of treated wood blocks, specifications 
were more rigid in limiting the amount of sap wood; but recent expe- 
rience seems to indicate that there is no noticeable difference in wear 
between heart and sap wood. 

1155. Causes of Decay. The decay of wood is due to a low 
form of plant life called fungi. Air, heat, and moisture are necessary 
for the existence of the fungous growth; and without any one of these 
the fungi can not live. Since air and heat are present in all climates, it 
is necessary to eliminate moisture to preserve the timber from decay. 
Seasoning, both air drying and kiln drying, is a method of removing 
part of the moisture, and hence is a method of preserving timber 
against decay; but any seasoned timber will re-absorb moisture, and 
hence seasoning is only an imperfect method of preservation. A 
more effective method is to inject into the timber some substance 
that will change the organic matter in the wood so it will no longer 
serve as food for the fungi. 

1156. The Preservative. The preservative performs two 
functions, viz.: (1) acts as an antiseptic to prevent decay; and (2) 
acts as a waterproofing material to keep out moisture. 

It is desirable that the preservative should be stable and remain 
in the block as long as possible; since where the travel is light, the 
life of the pavement depends upon the resistance of the blocks to 
decay. However, if an antiseptic has thoroughly penetrated the 
block, it will ordinarily be preserved against decay, even though a 
larger proportion of the preservative evaporates or is washed out. 



606 



WOOD-BLOCK PAVEMENTS 



CHAP. XIX 



But if the antiseptic evaporates or is washed out, the timber becomes 
again susceptible to changes in volume with changes of moisture 
content, which is objectionable in paving blocks. 

Any material that renders a block waterproof is in itself a fair 
preservative, even though it is not an antiseptic. For example, 
petroleum is a fair preservative of timber, although it is not anti- 
septic. If water could be kept entirely out of the block, there 
would be little or no decay; but this is practically impossible, since 
no amount of preservative will make wood absolutely waterproof. 

1157. Creosote is a distillate of coal tar, and is usually called 
creosote oil, and sometimes dead oil of tar. Creosote oil was the first 
material used for preserving paving blocks; and it is still the essen- 
tial constituent in all such preservatives. 

Creosote oil was not entirely satisfactory as a preservative for 
paving blocks. It preserved the wood and prevented decay; but 
it gradually evaporated and washed out, and permitted a change in 
the moisture content of the blocks, which caused expansion and con- 
traction. To remove this objection, coal tar was added to the 
creosote to increase the waterproofing qualities of the preservative. 
The addition of tar also cheapens the preservative. 

Coal tar may contain something Hke 40 per cent creosote oil, and 
hence is in itself a fair antiseptic ; but on the other hand, it is harder 
to force the viscous tar into the wood than the more fluid creo- 
sote oil. 

There is a considerable difference of opinion as to the relative 
merits of the different creosote preservatives. Some argue that the 
preservative should be pure creosote oil, having a specific gravity of 
1.03 to 1.07, and a few claim that it should have a higher specific 
gravity but still be free from tar; while others prefer a mixture of 
creosoted oil and coal tar having a specific gravity of 1.08 to 1.12, 
Most cities now use an oil having a specific gravity of 1.10 to 1.14 
and containing a large proportion of coal tar, which is usually re- 
quired to be nearly free from carbon. The presence of any consid- 
erable amount of carbon is likely to plug the pores of the wood and 
prevent the introduction of the preservative. 

Some engineers claim that water-gas tar (§ 564) gives satisfactory 
results, even though it has no antiseptic properties; but others claim 
that experience with this material has been too Umited in both extent 
and time to warrant its use on a large scale. It is usually cheaper 
than a mixture of creosote oil and coal tar. 

1158. Two proprietary methods of treating wood paving-blocks 



AKT. 1] MATERIALS AND TREATMENT 607 

were introduced comparatively early. One, called the kreodone 
process, consisted in impregnating block under pressure with a 
secret proprietary preservative. The other, called the creo-resinate 
process, consists in mixing melted resin and formaldehyde with the 
creosote, the resin being to waterproof the wood, and the formalde- 
hyde is to increase the antiseptic effect of the preservative. This 
process was very efficient, but was discontinued on account of the 
increase in the cost of resin. 

1159. Specifications for Preservatives. The specifications in 
§ 1160, § 1161, and § 1162, were prepared by the American Wood- 
Preservers' Association,* and have virtually been approved by prac- 
tically all of the national engineering societies interested in wood 
preservation.! 

1160. Creosote Oil. Creosote oil was formerly used for railway 
ties, structural timber and wood paving-blocks; but lately, owing to 
its scarcity and cost, has not been used much, particularly for paving 
blocks. Paving blocks do not recuire as perfect a preservative as 
ties and structural timber, since usurily their fife is hmited by their 
resistance to wear rather than to decay. Creosote oil when tested 
in accordance with the standard methods of the American Wood 
Preservers' Association, should comply with the following require- 
ments : 

"1. The oil shall be a distillate of coal-gas tar or coke-oven tar. 

"2. It shall not contain more than 3 per cent of water. 

"3. It shall not contain more than 0.5 per cent of matter insoluble in benzol. 

"4. The specific gravity of the oil at 38° C. compared with water at 15.5° C. 
shall be not less than 1.03. 

"5. The distillate, based on water-free oil, shall be within the following limits: 
up to 210° C. not more than 5 per cent; and up to 235° C. not more than 25 per 
cent. 

"6. The specific 'gravity of the fraction between 235° and 315° C. shall 
not be less than 1.03 at 38° C, compared with water at 15.5° C. The specific 
gravity of the fraction between 315° and 355° C. shall be not less than 1.10 at 
38° C, compared with water at 15.5° C. 

"7. The residue above 355° C, if it exceeds 5 per cent, shall have a float-test 
of not more than 50 seconds at 70° C. 

"8. The oil shall yield not more than 2 per cent coke residue." 

1161. Coal-tar Distillate Oil. Coal-tar distillate oil for paving 
blocks, when tested in accordance with the standard methods of the 



*Proccedings, 1917, p. 307-9. 
■flbid., p. 41 and 325. 



608 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

American Wood Preservers' Association,* shall comply with the fol- 
lowing requirements : 

"1. The oil shall be a distillate of coal-gas tar or coke-oven tar [§ 564]. 

"2. It shall not contain more than 3 per cent of water. 

"3. It shall not contain more than 0.5 per cent of matter insoluble in benzol. 

"4. The specific gravity of the oil at 38° C, compared with water at 15.5° C, 
shall be not less than 1.06. 

"5. The distillate, based on water-free oil, shall be within the following 
limits: up to 210° C. not more than 5 per cent; and up to 235° C. not more than 
15 per cent. 

"6. The specific gravity of the fraction between 235° and 315° C. shall be not 
less than 1.03 at 38° C, compared with water at 15.5° C. The specific gravity 
of the fraction between 315° and 355° C. shall be not less than 1.10 at 38° C, 
compared with water at 15.5° C. 

"7. The residue above 355° C, if it exceeds 10 per cent, shall have a float-test 
of not more than 50 seconds at 70° C. 

"8. The oil shall yield not more than 2 per cent coke residue." 

1162. Coal-tar Paving Oil. Coal-tar paving oil for paving blocks, 
when tested in accordance with the standard methods of the American 
Wood Preservers' Association,* shall comply with the following 
requirements : 

"1. It shall be a coal-tar product of which at least 65 per cent shall be a dis- 
tillate of coal-gas tar or coke-oven tar, and the remainder shall be refined or fil- 
tered coal-gas tar or coke-oven tar [§ 564]. 

"2. It shall not contain more than 3 per cent of water. 

"3. It shall not contain more than 3 per cent of matter insoluble in benzol. 

"4. The specific gravity of the oil at 38° C, compared with water at 15.5° C, 
shall be not less than 1.07 or more than 1.12. 

"5. The distillate, based on water-free oil, shall be within the following limits: 
up to 210° C, not more than 5 per cent; and up to 235° C. not more than 
25 per cent. 

"6. The specific gravity of the fraction between 235° and 315° C. shall be 
not less than 1.03 at 38° C, compared with water at 15.5° C. The specific 
gravity of the fraction between 315° and 355° C. shall be not less than 1.10 
at 38° C, compared with water at 15.5° C. 

"7. The residue above 355° C, if it exceeds 35 per cent, shall have a float-test 
of not more than 80 seconds at 70° C. 

"8. The oil shall yield not more than 10 per cent coke residue." 

1163. Water-Gas Tar. Refined water-gas tar shall conform "to 

the following requirements:! 

"1. The specific gravity shall be not less than 1.12 nor more than 1.14 at 
38° C, referred to water at the same temperature. 

♦Proceedings, 1917, p. 309-21. 

t Specifications for Creosoted Wood-block Paving, American Society of Municipal Improve^ 
ments, 1916, p. 5-6. 



ART. 1] MATERIALS AND TREATMENT 609 



"2. Not more than 2.0 per cent shall be insoluble by hot extraction with 
benzol and chloroform. 

"3. On distillation when made as hereinafter described,* the distillate, 
based on water-free oil, shall be within the following limits: up to 210° C, 
not more than 5.0 per cent; up to 235° C, not more than 15.0 per cent; up to 
315° C, not more than 40.0 per cent; and up to 355° C. not less than 25.0 per 
cent. 

"4. The specific gravity of the total distillate below 355° C. shall not be less 
than 1.0 at 38° C, referred to water at the same temperature. 

"5. The oil shall not contain more than 2.0 per cent water; and due allow- 
ance shall be made for aU water and insoluble foreign matter it may contain by 
injecting a corresponding additional quantity into the blocks." 

1164. Treatment of Blocks. There are two methods of 
treating the blocks with the preservative, viz.: (1) the open-tank 
process, and (2) the pressure process. 

1165. Open-tank Process. In this process the blocks are im- 
mersed in the preservative from a few minutes to an hour, depending 
upon the kind of wood and the degree of penetration desired. This 
method is largely used in France. In this country early in the his- 
tory of treated paving blocks, it was much used; but it is not now 
used. 

1166. Pressure Process. The standard specifications for the 
treatment of the timbers mentioned in § 1152, except Douglas fir, 
are substantially as follows: 

"The blocks are placed in a closed cylinder, and subjected to steam at a tem- 
perature of 220° to 240° F. for not less than 2 hours nor more than 4 hours. 
The steam and moisture are blown out of the cylinder, and then the blocks are 
subjected to a vacuum of not less than 22 inches of mercury for at least 1 hour. 
While the vacuum is still on, the preservative, heated to a temperature of 180° 
to 220° F., is run in until the cylinder is completely filled, care being taken that 
no air is admitted. Pressure is then gradually applied at a rate not to exceed 
50 lb. per square inch per hour, and is maintained at 100 to 150 lb. per square inch 
until the wood has absorbed the required amount of preservative. Next a sup- 
plemental vacuum of at least 20 inches is applied for at least 30 minutes. If 
desired this vacuum may be followed by a short steaming period. 

*'The timber may be either green or air reasoned; but should preferably be 
treated within three months after it is sawed. Green and seasoned timber shall 
not be treated together in the same charge. 

"After treatment the blocks shall show a satisfactory penetration of the pre- 
servative; and in all cases the preservative must be diffused throughout the sap 
wood. The surface of the blocks after treatment shaU be free from deposit of 
objectionable substances; and all blocks that have been materially warped, 
checked, or otherwise injured in the process of treatment shall be rejected." 

* Accompanying the printed specifications, but not reproduced in this volume. 



610 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

1167. The following are the reasons for the several steps in the 
treatment. 

The prehminary steaming softens or liquefies the sap, so it may 
later be removed from the pores of the wood. The steaming also 
equalizes the moisture content of heart and sapwood, which equalizes 
the resistance to penetration, and thus prepares the wood to receive 
the preservative more uniformly. The preliminary steaming is 
applied whether the timber is green or seasoned. In green timber 
the sapwood contains more water than the heartwood; and unless 
the excess sap is removed, the blocks will contain untreated, or at 
least under-treated, sapwood. Therefore, green blocks should be 
subjected to steaming and the vacuum process to remove the excess 
water from the sapwood. On the other hand, seasoned timber is 
more easily treated, i. e., takes the preservative more easily, than 
green timber. Sometimes seasoned timber accepts the preservative 
so easily that almost no pressure is required to produce the desired 
absorption; and consequently the easily treated portion receives too 
much preservative and the portion that is more difficult to treat 
receives too little. The sapwood is likely to be more thoroughly 
seasoned than the heartwood; and therefore the former may receive 
more preservative than the latter, and consequently the latter may 
decay because of incomplete penetration of the preservative. The 
steaming of seasoned blocks expands them, so that when treated and 
laid in the pavement they will have a minimum expansion with the 
absorption of moisture. Therefore, seasoned timber should be sub- 
jected to steaming to prepare it to receive the preservative and to 
decrease expansion when laid in the pavement. 

The preliminary vacuum is applied to remove the sap and mois- 
ture, which equaHzes the resistance to the penetration of the pre- 
servative. 

The preservative is applied under pressure and for a considerable 
time to secure complete penetration; but the pressure is applied 
slowly so as not to injure the strength of the wood. 

The supplemental or final vacuum is applied to equahze the distribu- 
tion of the preservative, but chiefly to remove the excess preservative 
in the outer portion of the block and thus decrease bleeding (§ 1211). 

The final steaming is applied to soften and remove the excess 
preservative from the surface of blocks. 

Finally, green and seasoned timber should not be treated together 
in the same charge, since they have unequal resistance to the pene- 
tration of the preservative. 



J 



ART. 1] MATERIALS AND TREATMENT 611 

1168. Amount of Preservative. The blocks laid in Indianapolis 
in 1896 (§ 1147) were treated by the open-tank process and contained 
only about 3 lb. of creosote oil per cubic foot. In the earlier appli- 
cations of the pressure process, the amount was usually 10 to 12 lb. 
per cubic foot; but later the general practice was to inject from 20 to 
24 lb. per cubic foot, which resulted in a greatly increased cost and 
an excessive bleeding of the blocks (§ 1211). Recentty the tendency 
has been to reduce the absorption; and at present the average is 
about 16 lb. of water-free preservative per cubic foot. The standard 
specifications of the American Wood Preservers' Association and also 
those of the American Society of Municipal Improvements require 
16 lb. per cubic foot. 

The amount absorbed is determined from gages on the treat- 
ing cylinder and a knowledge of the volume of the charge; and may 
be checked by weighing several blocks before and after treatment. 

1169. Testing the Blocks after Treatment. Usually the only 
test made is to determine the penetration of the preservative. '' To 
determine this, at least twenty-five blocks shall be selected from 
various parts of each charge, and sawn in half at right angles to the 
fibers, through the center; and if more than one of these blocks show 
untreated sap wood, the charge shall be retreated." 

1170. Occasionally a test is made to determine the amount of 
water a treated block will absorb. The usual specifications for this 
test are: " The treated blocks after being dried in an oven at 100° F. 
for 24 hours, and then immersed in clear water for 24 hours, shall not 
absorb more than 3| per cent of their dry weight if pine, nor more 
than 4 J per cent if tamarack." This test is to determine the pos- 
sibihty of the block's swelHng after being laid, by the absorption of 
moisture; and therefore is quite important. The absorption will 
increase with the time after treatment; and therefore the blocks for 
this test sho lid be taken from those about to be laid rather than 
from those recently treated. 

The results by this test depend more upon the time since treat- 
ment and upon the method of storage than upon the method of 
treatment; and hence this is not an accurate test of absorbing power. 
Further, since no preservative process can make blocks absolutely 
waterproof, they should be so laid as to reduce to a minimum the 
amount of moisture absorbed (see § 1180). 

1171. Care of Blocks after Treatment. The blocks should prefer- 
ably be laid in the street as soon as possible after being treated. If 
they can not be laid within two days, provision should be made to 



612 WOOD-BLOCK PAVEMENTS [cHAP. XIX 

prevent them from drying out, by stacking in close piles and covering 
them ; and if possible, sprinkhng them thoroughly at intervals. To 
prevent expansion in the pavement through the absorption of water, 
the blocks should be well sprinkled about two days before being laid. 



Art. 2. Construction 

1173. Foundation. The subgrade should be prepared as 
described in Art. 1 of Chapter XV, — Pavement Foundations. The 
usual foundation is a layer of hydrauhc concrete, which should be 
constructed as described in Art. 2 of Chapter XV. 

The specifications of the American Society of Municipal Improve- 
ments state: ''At no place shall the surface of the finished concrete 
vary more than a half inch from the given grade." 

1174. Bedding Course. A bedding course is necessary to 
compensate for any unevenness in the top surface of the concrete 
foundation and to afford a good bearing for the blocks. Three 
forms of bedding course are in common use, which for brevity may 
be designated as sand, hydrauHc-cement mortar, and bituminous 
cement. 

1175. Sand Cushion. The sand bedding-course varies in thick- 
ness from 1 to 2 inches. The disadvantages of a thick sand cushion 
are very much the same for wood blocks as for brick — see § 977. 
In recent years, as in brick pavements, there has been a tendency to 
reduce the thickness of the sand cushion. The 1916 specifications 
of the American Society of Municipal Improvements require a 
cushion 1 inch thick, of '' sand that will pass a J-inch screen and 
contain 10 to 25 per cent of loam or clay." The sand cushion should 
be struck with a template to a surface parallel to the grade and con- 
tour of the finished pavement; and should then be rolled. 

Sometimes, instead of striking the sand cushion with a template, 
screeds are laid transversely across the pavement at intervals of 8 or 
10 feet, being placed upon a ridge of sand or mortar so as to bring the 
top surface of the screed parallel to, and at the right distance below, 
the surface of the pavement. The sand is spread between the screeds, 
and then struck off to the right depth with a straight edge which 
rests upon the screeds and is kept parallel to the curb. This method 
requires more labor and does not give as accurate a surface as striking 
with a template. The only disadvantage of using a template is 
that a new one is required with each change in crown or width, 



ART. 2] CONSTRUCTION 613 

although this objection is overcome in part by using a template 
which is shghtly adjustable. 

1176. Substantially all of the comments concerning the sand 
cushion for brick pavements (§ 971-78) apply also to that for wood- 
block pavements. In addition, a sand cushion holds moisture, and 
hence increases the absorption of the blocks and adds to the troubles 
due to their expansion in the pavement. Formerly the sand cushion 
was the most common form of bedding course; but it has now prac- 
tically been abandoned. 

1177. Djy-mortar Bed. The method of laying wood blocks on a 
dry-mortar bed is substantially the same as for laying bricks on a 
cement-sand bedding course (see § 979-81). It would be possible 
to lay wood blocks upon a wet-mortar bed by either of the processes 
employed for brick pavements (see § 982) ; but it is not known that 
it has ever been done. 

The 1916 specifications of the American Society of Municipal 
Improvements for preparing the dry-mortar bed for wood blocks are 
as follows: 

"The concrete foundation shall be cleaned and swept; and shall be thor- 
oughly dampened immediately in advance of the spreading of the cushion course. 
Upon the surface of the foundation thus prepared shall be spread a layer of mortar 
not exceeding | inch in thickness, made of one part portland cement and three 
parts of sand. Only sufficient water shall be added to this mixture to insure a 
proper setting of the cement, the'intention being to produce a granular mixture 
which may be raked or struck by a template to the desired grade. The mortar 
shall be [thoroughly mixed, and shall be spread in place upon the foundation by 
means of a template immediately in advance of the laying of the blocks." 

1178. It is doubtful if the mixture of cement and sand ever gets 
enough water to cause it to set fully, since the joints between the 
blocks are quite narrow. The only reason for using a granular mix- 
ture is that it can be spread and struck easily; but the ordinary 
cement mortar containing enough water to insure a complete set, 
can be spread and struck without serious trouble. Or, better still, 
if the concrete foundation is finished with a shght excess of mortar on 
the surface, the wood blocks can be set in the mortar as are the 
brick in the monohthic brick pavement (§ 892). 

An objection to the mortar bedding course is that the pavement 
can not be used until the mortar has set; but if the mortar bedding 
course is laid immediately after the concrete foundation is placed, this 
objection is eliminated. 

A serious objection to the dry-mortar cushion is that not enough 



614 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

water is used to secure a good quality of mortar. When the dry- 
mortar cushion is used for a brick pavement, the mortar is thor- 
oughly wet b}^ sprinkling the brick after they are laid; but this 
should not be done with wood blocks, since they absorb more water, 
and since with wood blocks the joints are usually filled with bitumi- 
nous cement (§ 1187), which should be applied only when the blocks 
are dry. 

1179. Bituminous Bed. If the top of the concrete foundation 
has not been finished to an accurate surface by strkiing with a tem- 
plate (§ 461-62), it should be leveled up by spreading a layer of 1 : 2 





^ 

c 


f. 


h^. 




■^^^^ 




^^ 


- 


■*-^-^ 


m^ 









Fig. 224. — Finishing ISIgrtae Bedding-course -^vith a Steel Float. 

cement mortar on it. This mortar should be of such consistency 
that it maj^ be easily spread; and should be applied to the surface 
of the concrete before initial set of it has begun. The mortar should 
be then worked to an accurate surface by means of a long-handled 
wood float having upturned ends. When finished the surface should 
not show any depressions greater than J inch under a 5-foot straight 
edge laid parallel to the curb. Fig. 224 shows the method of 
finishing the mortar bedding-course with steel floats; and Fig. 225 
shows the method of finishing the bedding course with a wood- 
float. 

1180. After the concrete base and the mortar coat have set and 
hardened, and after the surface has been thoroughly cleaned, and 
while it is perfectly dry, a coat of coal-tar pitch is spread upon the 
surface. The pitch should meet the specifications of § 576-77 



ART. 2] 



CONSTRUCTION 



615 



(page 295) for filler for wood blocks ; and should be applied at a 
temperature between 250° and 300° F. It should be spread to a 
uniform thickness of not more than J inch, and be finished to a smooth 
surface. The blocks should be set directly upon this paint coat 
within 30 minutes after it has been applied. If the work is properly 
done, the blocks are firmly held in place; and in tearing up such a 
pavement it is not unusual to have the pitch pull up a film of the 
concrete base. If the surface of the concrete or the mortar coat 
has ridges or depressions in it, the blocks are likely to split under 
travel. If the pitch coat is thicker than | inch, it is likely to flow 




Fig. 225. — Finishing Mortar Bedding-course with a Wood Float, 



and split the blocks. The slipping of the blocks on the pitch coat is 
sometimes called " floating." 

The chief advantage of the bituminous bedding course is that 
the bituminous cement completely seals the pores of the block, and 
prevents the absorption of any water that may reach the top of the 
concrete base through cracks in the wearing coat. This method 
represents the best modern practice, and has recently been adopted 
quite generally. 

1181. Laying the Blocks. Upon one of the three bedding 
courses described above, the blocks are set with the fiber vertical, 
in straight parallel courses, leaving a space at the curb 1 inch in 
width for the expansion joint. The blocks are laid ''hand tight"; 
but each eight or ten courses are driven together by laying a 4- by 



616 



WOOD-BLOCK PAVEMENTS 



[chap. XIX 



4-inch scantling against the last course and striking it with an axe or a 
sledge. No joint should be more than | of an inch in width, although 
some good authorities permit a width of Ye of ^^ inch. The blocks 
should lap at least 2 or 2J inches. Only whole blocks should be used, 
except in starting and closing a course. The block used in starting 
or closing should have its cut face perpendicular to the top. In 
placing the blocks the workman should stand upon the blocks already 
placed, and never upon the bedding course. 

There is no agreement as to whether the courses shall be per- 
pendicular to the curb, or at an angle of 45° or 67J°. It is claimed 
that if the courses are obHque to the curb, the wear at the joints, par- 
ticularly the transverse ones, will be less than if the courses are per- 
pendicular to the curb. But this claim has not been estabHshed; 
and as it is most convenient and costs about 2 cents per square yard 
less to lay the courses at right angles to the curb, this method has 
generally been adopted. 




Fig. 226. — Laying Wood-block Pavement between Street-car Rails. 



1182. Fig. 226 shows the method of laying wood blocks between 
the rails of a street-car track on a mop coat of tar over a smooth 



ART. 2] 



CONSTRUCTION 



617 



concrete base. Fig. 227 shows the manner of laying wood blocks 
between the railway area and the curb. Note the plank next to 
the curb to provide space for the longitudinal expansion joint. 
The blocks are being laid on a mop coat of tar on a concrete base. 



MM 






■tt 










"A. . 


^ 


m 


■ 


1 






w 


f^^^A 


-;^ <^,; 








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1 


1 


W 










M 




^K 




m 


^ 


1 






^^S 






qj^p 




L^, 








- 










t\ 


-> 




















J 


■■ "^i«-. 






















r^ 



Fig. 227. — Laying Wood-blocks on a Mop Coat of Tar. 



1183. Rolling. After being placed, the blocks are inspected, and 
the rejected blocks are removed and replaced with acceptable ones. 
The surface should then be swept clean, and be rolled with a tandem 
roller weighing from 3 to 6 tons. The roller should begin at the side 
of the pavement, run slowly parallel to the center hne, and work 
inwardly until the center of the road is reached. It should then move 
to the opposite side of the pavement and proceed as before. As the 
roller passes back and forth, it should overlap its course each time. 
After one rolhng of the entire surface, the speed of the roller may be 
increased and the rolUng continued imtil the blocks are thoroughly 
and evenly bedded. 

Portions of the pavement inaccessible to the roller should be 
thoroughly rammed with a paver's rammer (§ 992) weighing not less 
than 50 lb., striking upon a plank not less than 6 feet long, 10 to 12 
inches wide, and 2 inches thick. The plank should be laid parallel 
to the curb, and moved so that the surface will be equally rammed 
and brought to the proper elevr.tion. 



618 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

If the bedding course is green mortar, the rolHng should be com- 
pleted before the mortar has set. 

When the rolling and ramming are completed, the surface of the 
pavement should conform so nearly to that indicated on the plans, 
that it will nowhere depart more than one fourth of an inch from 
properly formed templates or from a 10-foot straight edge applied 
parallel to the center line. 

1184. Joint Filler. The joints between the blocks are filled 
with grout, sand, tar pitch, or asphalt. 

1185. Grout. Occasionally the attempt is made to fill the joints 
of a wood-block pavement with hydraulic-cement grout; but if the 
blocks are set as closely together as they should be, the joints will be 
so narrow that it is impossible to get a good grout to fill them. If 
the grout is thin enough to flow into narrow joints, it will not con- 
tain enough cement to make it of much, if any, value; and besides 
it will not adhere well to the sides of treated wood-blocks, and even 
the preservative seems to kiU the cement. 

1186. Sand. Fine clean dry sand is swept into the joints; and 
the surface is covered with sand to the depth of J an inch. The 
sand is placed upon the surface to insure that every joint is filled 
and to permit travel to grind the sand into the surface of the blocks. 
After the sand has remained on the pavement for a time, depending 
upon the density of the travel, it is swept up and hauled away. 

Sand was formerly the most common joint filler, but it has 
practically been abandoned. It is cheap and makes a fairly water- 
tight pavement; but it has little or no effect in binding the blocks 
together to prevent settlement due to shrinkage of the sand cushion 
(§ 1055) or other causes (§ 1056-57), or to prevent upheavals 
(§ 1060). 

1187. Tar Pitch. The tar-pitch filler should conform to the spe- 
cifications stated in § 576-77, page 295. It is heated in kettles or 
tanks on the street. The temperature should never exceed 325° F.; 
and it should be applied to the pavement at a temperature between 
250 and 300° F. The hot pitch may be poured into the joints as 
described for brick pavements (see the second paragraph of § 1011). 
Fig. 228 shows a somewhat antiquated method of applying the filler 
to a wood-block pavement. This method is more suitable for a 
brick pavement than a wood one, since with the former the joint is 
wider, and hence it is easier to follow a joint with the point of the 
can; and also since more tar is required, and hence the tar flows 
better through the tip of the can. 



ART. 2] 



CONSTRUCTION 



619 




Fig. 228. — Filling the Joints with a Conical Can. 



Fig. 229 shows a better method of applying the tar joint-filler. 




Fig. 229. — Applying Tar Joint-filler with Bucket and Squeegee. 



620 



WOOD-BLOCK PAVEMENTS 



[chap. XIX 



Fig. 230 shows a buggy for transporting and applying pitch joint- 
filler. 



t 




Fia. 230. — Buggy for Applying Pitch Joint-filler. 



Fig. 231 shows the finished wood-block pavement. 




Fig. 231, — Finished Wood-block Pavement. 

1188. In fining the joints care should be taken to leave as little 
bituminous cement on the surface as possible, since one of the ob- 
jections to a treated wood-block pavement is that the preservative 
exudes, i. e., " the pavement bleeds," and covers the surface with a 
sticky mass (§211). If any joint filler is left upon the surface, it 
increases^this objection. Further, some object to a bituminous filler, 
because it is liable to be forced out of the joints onto the surface of the 



fl 



ART. 2] 



CONSTRUCTION 



621 



pavement. An advantage of a bituminous filler is that it virtually 
surrounds each block with an expansion joint, and hence decreases 
the expansion due to the absorption of moisture by the blocks. 

Under no circumstances should the pitch be applied when there 
is any moisture in the joints; and therefore a pitch filler should not 
be used with a cement-sand bedding course (§ 1177). 

1189. The specifications of the Ohio Department require that 
the lower half of the joints shall be filled with tar pitch as in § 1187, 
and the upper half with sand as in § 1186. 

1190. Open- JOINT Construction. Since a wood-block pave- 
ment made as described above is quite smooth, it is customary to 
modify the construction on steep grades so as to give a good foothold 
to horses. Such construction is not employed unless the grade is 
more than 3 or 4 per cent — see Table 15, page 57. 

Formerly a corner was cut out of the upper edge of a block 
as shown in Fig. 232 so as to give an open joint i inch wide and 




Fig. 232. — Rectangular Wood-block Pavement with Open Joints 



IJ inches deep; but at present it is more common and cheaper 
to place between adjacent courses a creosoted wood lath ye oi an inch 
thick and 2 inches wide. The joint is poured about half full of 
bituminous filler; and then the space above the lath is filled with 
hot crushed stone, and the interstices between the stones are filled 
with bituminous cement. 

Sometimes the upper edge of the face of the blocks is chamfered 
at an angle of about 45° to a depth of about f of an inch; and this 
space is filled with the ordinary joint filler. This method is not as 



622 WOOD-BLOCK PAVEMENTS I CHAP. XIX 



satisfactory nor as cheap as the second one described in the preceding 
paragraph. 

1191. Expansion Joints. The expansion of wood paving- 
blocks due to changes of temperature is not great enough to require 
any consideration; but the expansion and contraction due to change 
in the moisture content requires attention. The amount of expan- 
sion and contraction due to moisture depends somewhat upon the 
method of treatment. If the blocks are seasoned before being treated, 
and are not steamed before they are impregnated with the preserva- 
tive, they are hkely to absorb moisture and swell after the preserva- 
tive has evaporated. Again, with green timber the steaming and the 
vacuum Uquefies and removes the sap, and reduces the volume of the 
wood so it will be less Hkely to shrink when laid in the pavement. 
Finally, the amount of preservative should be such as to fill the cells 
of the wood and cover the fibers, thus making the blocks partially 
waterproof. An additional means of reducing the expansion and 
contraction due to moisture is to lay the blocks in a paint or mop 
coat of bituminous cement (see § 1179-80). 

1192. To allow for expansion due to temperature and moisture, 
it is customary to construct a longitudinal expansion joint next to 
each curb. There are two forms of expansion joints, the poured and 
the pre-moulded. 

The poured joint is made by placing a | or a 1-inch board next 
to the curb, and setting the blocks against it (see Fig. 227, page 617); 
and after the blocks are set and the joints are filled, the board is 
removed and the space is filled with bituminous joint-filler poured hot 
(see Fig. 233). For an illustration of a brick pavement showing a 
thin board in place with wedges behind it to facilitate its removal, 
see Fig. 171, page 483. 

The pre-moulded expansion joint is a sheet of felt or its equivalent 
saturated with tar pitch or asphalt. There are several somewhat 
similar forms on the market. For a few additional items concern- 
ing pre-moulded expansion joints, see the second paragraph of 
§ 1017. 

1193. Formerly transverse expansion joints were inserted in 
wood-block pavements; but they have been discontinued, because 
they are not needed, and are a positive detriment. The objections 
to the transverse expansion joint for wood-block pavements are sub- 
stantially the same as for brick pavements — see § 1018. 

Care should be taken to fill the joints around manholes, water- 
boxes, etc., to prevent water's reaching the foundation, where it will 



ART. 2j 



CONSTRUCTION 



623 



freeze and lift the pavement, or be absorbed by the blocks and cause 
them to expand. 

1194. Crown. The surface of a wood-block pavement should be 
quite smooth; and therefore the crown should be comparatively 
small. A special committee of the American Society of Civil Engi- 
neers recommended that the transverse slope be between J and | of 
an inch per foot — see Table 16, page 65. 

1195. Maximum Permissible Grade. The maximum per- 
missible grade for a close-joint wood-block pavement is 3 or 4 per 
cent (see Table 15, page 57); and with the open-joint construction 
(§ 1190), the maximum grade may be 6 or 7 per cent. 




Fig. 233. — Pouring the Longitudinal Expansion Joint. 



1196. PAVING Adjacent to Track. Wood-blocks are laid 
adjacent to the rails of street railway tracks in substantially the same 
m.anner as bricks — see Fig. 196 and 197, page 540. 

1197. Cost of Construction. Price of Blocks. Table 70, 
page 624, shows the market quotation for treated wood paving- 
blocks for November 1, 1917. For more recent quotations, see con- 
struction news in current technical journals. 

1198. Cost of Pavement. The following estimate was prepared 
for this volume by a specialist in wood preservation and wood paving 
who has no financial interest in contracting.! 

1199. Cost of Blocks. Table 71, page 624, shows the amount of 
timber and preservative required. The method of using Table 71 in 

t Mr. Walter Buehler, Mem. Amer. Soc, of Civil Engrs., Chicago, 



624 



WOOD-BLOCK PAVEMENTS 



[chap. XIX 



TABLE 70 
Makket-price for Treated Wood Paving-blocks* 




Locality. 


Absorption, 
lb. per cu. ft. 


Depth, 
inches. 


Price, 
per sq. yd. 


New York City 


16 
16 
16 
16 
16 
16 
16 
16 
16 
16 
16 


31 

4 

4 

3^ 

4 

4 

3^ 

3 

31 

4 

4 


$2 00 


(( u n 


2 25 


Chicago 


1 85 


St Louis . ... 


1 80 


it a 


2.03 


Kansas City 


2.50 


St. Paul 


2.00 


San Francisco 


2.15 


'i a . ' •' 


2 26 


i- It 


2.57 


Seattle 


2.35 







ha 



TABLE 71 
Amount of Lumber and Preservative Required for Paving Blocks 



Depth of 
Block, 
Inches. 


Lumber Required, 
Feet, B.M., per Sq. Yd. 


Preservative Required, 
Gallons per Sq. Yd. 


Net. 


Waste. 


Total. 


Absorption, Lb. per Cu. Ft. 




10 


12 


16 


3 

3^ 
4 


2 7 
31.5 
36 


2.7 

3.15 

3.6 


30 
35 
40 


2.443 
2.862 
3.274 


2.945 
3.546 
3.928 


3.928 
4.583 

5.238 



determining the cost of blocks is as follows: Assume the cost of 
lumber at the treating plant at $30 per thousand feet, B. M., which 
under normal conditions prevailing a few years ago would not be over 
$25. Assume that the preservative meets the specifications of 
§ 1161; and that it costs 9 cents per gallon. Assume that the blocks 
are to be SJ inches deep, and are to be treated with 16 lb. per cubic 
foot. The cost of the blocks are: 

Lumber 35 feet B.M., at $30 $1 .05 per sq. yd. 

Preservative 4.583 gallons at 9 cents 414 '' 

Labor, depreciation, interest, etc 240 " 



Factory cost $1 . 704 " 

Profits at 15 per cent gross 30 " 

Factory selling price $2 . 004 " 

The approximate weight of wood blocks treated with 16 lb. per 
cubic foot is as follows: 3-inch, 130 lb. per square yard; 3J-inch 
150 lb. per square yard; and 4-inch, 170 lb. per square yard. 

* Engineering News-Record, Vol, 79 (1917), Constryction News, p, 180, 



ART. 2] 



CONSTRUCTION 



625 



1200. Cost of Wearing Coat. Table 72 shows in detail the esti- 
mated cost of a 3|-inch wood-block pavement with two forms of bed- 
ding course. 

TABLE 72 
Estimated Cost of 3 2 -inch Wood-block Pavement 



Items. 



Sub-grade, see Table 56, page 546 

Concrete Foundation, see Table 56, page 546 

extra finish to surface 

Bedding Course, 1 : 4 dry cement and sand 

. 5 gallon of pitch, and labor 

Wood Blocks, see § 1199 

freight, saj'', 200 miles at 6 cents per 100 blocks . 

hauling, at 60 cents per hour 

laying, at 25 cents per hour 

rolling. 

Joint Filler, including longitudinal expansion joint. 
Top Dressing, purchasing and spreading sand. . . . . 



Total cost, exclusive of interest, insurance, deprecia- 
tion, profit, etc 



Bedding Course. 



Tar Paint 
Coat. 



$0,217 

.568 
.01 



.06 
1.004 
.09 
.05 
.08* 
.01 
.12 
.02 



$3,229 



Dry Mortar. 



$0,217 
.568 

.18 

2.004 
.09 
.05 
.08* 
.02 
.12 
.02 



$3,349 



1201. Example of Cost. Table 73, page 626, shows the cost of 
laying 150,000 square yards of creosoted wood-block paving in 
Minneapolis by city force, and are given in unusual completeness, and 
hence are specially valuable in making estimates. 

1202. The following are the details of the cost of lajang a wood- 
block pavement in Cambridge, Mass., in 1913. f Common labor 
was 31 cents per hour. The foundation consisted of 5 inches of 
1 : 2| : 5 concrete; and the bedding course was 1 inch of cement and 
sand. The blocks were southern long-leaf yeUow pine treated with 
20 lb. of preservative. The joints were filled with 1 : 1 cement 
grout. Longitudinal expansion joints were provided at each curb, 
and transverse contraction joints at each 30 feet. 4-inch blocks cost 
$2.59 per square yard dehvered on the street, and $4.11 per square 
yard complete in the pavement; and 3j-iLch blocks cost $2.29 and 
$3.81, respectively. 

1203. Contract Price. Table 74, page 627, shows the contract 
price of wood-block pavements in various cities, and incidentally 
also gives considerable information as to the details of practice of 
these cities. 



*If there is a street-railway track, add 2 cents. 
fEngineering News, Vol. 71 (1914), p. 1131. 



626 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

TABLE 73 
Cost of Wood-block Pavement in Minneapolis* 

Items. Per Sq. Yd. 

Sxjbgrade: grading and shaping , $0.2 87 

Concrete Base, 1:3:6, 6 inches thick: 

cement, $1.12 per bbl., f.o.b. cars 1222 

sand $0 . 60 per cu. yd., dehvered 0395 

stone, $1.00 per cu. yd., f.o.b. quarry, $1.70, dehvered 2386 

labor mixing and placing by hand at 28 cents per hour 1392 

hauling cement, plank, etc., at 59 cents per hour .0238 

concreting strip 1| ft. wide between railway ties 0189 

Total for concrete base $0 . 5822 

Sand Cushion, 1 inch : sand at 60 cents per cubic yard on job $0 . 200 

Wood Blocks, Norway pine and tamarack : 

4-inch, treated with 12 lb. of creodone creosote 1 .3275 

[ hauling blocks at 59 cents per hour 0495 

laying blocks at 22^° with curb, at 40 cents per hour 0716 

Total for blocks $1 . 4486 

Joint Filler, sand and pitch: 

sand at 60 cents per cu. yd., on job , 0055 

pitch at 5- 7 cents per gallon 0490 

labor at 28 cents per hour 0175 

Total for filler $ .0720 

Headers : 

4 X 10-inch plank at cross streets and alleys 0030 

M ISCELL ANE ous : 

materials „ ...,.'.. . 0077 

labor 0002 

cleaning up 0071 

tools 0200 

Total miscellaneous $ . 0350 

Total average cost .' $2 . 3795 

1204. Merits and Defects. The merits of a treated wood- 
block pavement are: 1. It has a smooth surface, and therefore is a 
quiet pavement. It is less noisy than sheet asphalt, brick or stone- 
block; and from the standpoint of tenants, this is an important 
advantage. 2. It is a reasonably durable pavement, even under 
heavy and dense travel. This conclusion has been established in 
many cities in this country and in Europe. 3. The pavement is 
easy to clean; and its surface does not grind up and make dirt. 4. 
It has a low tractive resistance. 

*B. H. Durham, Street Engineer, in Engineering and Contracting, Vol. 35, p. 451. 



ART. 2] 



CONSTRUCTION 



627 



TABLE 74 

Contract Price op Wood-block Pavements in Various Cities* 

Laid in 1912 



Locality. 


Amount. 
Laid in 

1912, 
Sq. Yd. 


Concrete Base. 


Kind 

of 
Filler. 


Guar- 
antee, 
Years. 


Total 
Thick- 
ness, 
Inches. 


AVER- 


State. 


City. 


Thick- 
ness, 
Inches. 


Propor- 
tions. 


Pbice. 

Per 
Sq. Yd.i 


Connecticut. . . 


Bridgeport. . . 
S. Norwalk. . . 


10 300 
3 400 


6 
5 


1:3:6 
1:3:5 


sand 
sand 


5 
5 


91 


$3.10 
3.19 


Georgia 


Albany 


10 000 


5 


1:3:6 


sand 




9 


2.18 


Illinois 


Granite City . 
Quincy 


10 000 
9 171 


6 
5 


1:3:5 
1:3:6 


pitch 
asphalt 


■■■-■■ 


10- 

92 


2.542 
2.66 


Iowa 


Burlingtor. . . 


22 000 


6 


1:3:6 


asphalt 


5 


lOi 


2.77 


Kentucky. . . . 
Louisiana 




1 578 








5 




2.852 


New Orleans . 
Shreveport. . . 


18 401 
54 000 


6 
5 


1:3:6 
1:3:5 


pitch 
sand 


3 


10 

8 


3.002 
2 24 


Maine 


Bangor 


1 700 


6 


1:3:6 


pitch 


5 


91 


3.88 


Mass 


Springfield . . . 

Hibbing 

Minneapolis. . 
Owatonna. . . 
Virginia 


12 949 













3 13 


Minnesota. . . . 


44 608 

130 000 

29 1843 

22 854 


5 

■■■-•■ 

6 


1:3:6 
1:3:6 
1 :8 
1:2:4 


asphalt 
pitch 
pitch 
pitch 


5 


9§ 


2.77 
2.43 




5 
5 


9^ 
101 


2.292 
2.692 


Mississippi. . . 


Greenwood. . . 


25 000 


6 


1:3:5 


bitu. 


5 


11 


2.422 


Missouri 


Kansas City. . 


1021 


6 


1:3:6 


sand 


5 


11 


2.95 


Montana 


Miles City . . . 


4 5003 


5 


1 :6 


asphalt 


3 


9 


3.202 


New Jersey . . . 


Jersey City. . . 


11891 


•5 


1:3:5 


sand 




n 


3.00 


New York 


Plattsburg . . . 
Rochester. . . . 


1979 
8 392 


6 
6 


1:3:6 
1:3:6 


sand 
sand 


3 
5 


10 
lOi 


3.083 
3.32 


S. Carolina. . . 


Charleston. . . 


9 000 


4 


1:3:5 




5 


8 


2.723 


Texas 


Brownsville. . 

Hamilton .... 
Vancouver. . . 


29 000 

12 000* 
189 875 






sand 






2.70 


Canada 


6 
6 


1:3:6 

1 : 2i : 5 




10 
101 


2.85 




pitch 


5 


3.202 



1 Including grading and concrete base 2 Exclusive of grading. 3 3-inch block * 20 lb. per cu. ft. 

The defects of a treated wood-block pavement are: 1. It is some- 
what shppery, particularly when its surface is moist. In this respect 
it is about on a par with sheet asphalt. 2. Its surface is liable in 
hot weather to become covered with a sticky mass which adheres to 
wheels of vehicles and tracks into houses (§1211). 3. It is rather 
high in first cost. 

1205. Specifications. The American Society of Municipal 
Improvements in 1916 adopted complete specifications for Creosoted 
Wood-block Paving; and substantially the same specifications have 
been adopted by the American Wood Preservers' Association and 

* Engineering and Contracting, Vol. 39 (1913), p. 380-81, 



628 



WOOD-BLOCK PAVEMENTS 



[chap. XIX 



other associations interested in wood paving. Copies of these speci- 
fications may be had for a nominal sum of the secretary of the first- 
mentioned society. 

Art. 3. Maintenance 

1206. The experience with treated wood-block paving has been 
comparatively short, and hence there has not been developed any 
general method of maintenance or repairs. 

1207. Defects to be Removed. The principal matters 
requiring attention are: removing poor blocks, raising low spots, 
re-laying over trenches, lowering bulges, removing exudation. 

1208. Removing Poor Blocks. Blocks fail owing to defects in 
the timber or to imperfect treatment. The latter do not usually 
appear until after the pavement is several years old. Generally, 
only a portion of a single block fails, and usually only a few blocks 
in each city block. Fig. 234 shows the failm*e of a single block; 




Fig. 234. — Failure of a Block on Westminster Place, St. Louis. 

and Fig. 235 shows the failure of several blocks. Not infrequently 
the faiUng blocks are in a bunch, indicating that there was prob- 
ably something wrong with a single charge. The failure or decay 
is ordinarily due to insufficient preservative in either the sap- 



I 



A.HT. 3] 



MAINTENANCE 



629 



wood or the heartwood (see § 1167). At first the hole is small and 
shallow, and does no great harm, although it gradually enlarges, par- 
ticularly if there is much heavy steel-tired traffic. The defect can be 
temporarily cured by filling the hole with bituminous joint-filler 




-7L 



\ 



Treated in 1903. Photographed in 1915. 
Fig. 235. — Failure of Several Blocks on Westminster Place, St. Louis. 



or better with mortar or fine concrete made with bituminous cement. 
The only permanent remedy is to cut out the defective block and 
replace it with a good one, which can be done easily and quickly. 
With a little care and attention a new block can be inserted so that 
the patch is hardly visible. 

1209. Raising Low Spots. Frequently shallow depressions appear 
in the pavement. These holes may be due to the settlement of the 
foundation (§ 1056), to the settlement of the soil in a trench (§ 1057), 
or to the shrinkage or shifting of the sand cushion (§ 1055). Such 
holes are objectionable because they are unsightly, particularly when 
filled with water; and they hold water which dissolves the preserva- 
tive, and also causes the blocks to swell and perhaps buckle. The 
sinking of the blocks break the bond of the joint filler, particularly 
if it is not bituminous; and may permit water to reach the founda- 
tion, which if it freezes may lift the pavement. The remedy is to 
take up the spot, remove the cause and re-lay the blocks. For a 



630 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

discussion of precautions to be taken in re-laying a brick pavement 
under similar conditions, many of which are equally applicable in re- 
laying wood-block pavements, see § 1061. 

1210. Re-laying over Trenches. It is frequently necessary to re- 
lay a wood-block pavement over a trench on account of the settle- 
ment of the soil in the trench or because a trench is opened to 
repair or lay a pipe or sewer. For a discussion of the method of re- 
laying a brick pavement over a trench, see § 1061. 

1211. Lowering Bulges. A bulge or ridge is sometimes formed 
in a wood-block pavement by the expansion due to the absorption of 
moisture. If the pavem entis not provided with adequate longitudi- 
nal expansion joints, the bulge may be longitudinally along the crown 
of the pavement; or a bulge may take place at a raised footway 
crossing or at the crown of an intersection pavement (see § 1060). 
Usually a bulge can be replaced by removing a few blocks along the 
crest of the bulge, pressing the adjoining pavement back to place, and 
re-laying the blocks that were removed. 

1212. Bleeding. In some cases the preservative fluid oozes out 
of the blocks and forms a thick sticky mass on the surface of the 
pavement, which is picked up by the wheels of passing vehicles and is 
tracked into houses. When this occurs the pavement is said to 
bleed. The bleeding may be due to one or more of the following 
causes, viz.: 1. The expansion by heat of the air in the pores of the 
block may force out the preservative. 2. The absorption of moisture 
by one part of a block or one portion of the pavement may cause an 
expansion which forces the preservative out at some other point. 
3. Too much preservative may have been injected. 

Steaming and the vacuum treatment of green blocks decreases the 
bleeding by removing the air from the cells and by reducing the 
absorption of preservative in the sapwood; and the steaming of 
seasoned blocks reduces bleeding by expanding the blocks to their 
maximum size so that when laid they will be less likely to expand 
by the absorption of moisture. The bleeding occurs only in hot 
weather. The character of the preservative makes little or no dif- 
ference in the amount of bleeding, many claims to the contrary not- 
withstanding. Apparently a pavement bleeds less under heavy than 
under light travel, partly because the traffic seals the pores of the 
wood and prevents the oil from escaping, and partly because passing 
wheels carry away the sticky materials as rapidly as it oozes out. 

1213. The remedy for a bleeding pavement is to sprinkle it with 
fine dry sand, and remove the sand after it has absorbed the bitumi- 



ART. 3] MAINTENANCE 631 

« — ___ — . — _ 

nous material. In extreme cases it may be necessary to apply a 
second coat of sand. Usually the worst cases do not bleed after 
the first year or two. 

1214. Cost of Maintenance. There is an unfortunate 
dearth of data concerning the cost of repairs or of maintenance of 
any pavement; but the lack is greater for treated wood-block pave- 
ments than for any other kind, since the experience with such pave- 
ments is comparatively limited (§ 1147), and since most such 
pavements have been laid under a 5-year guarantee. 

The following examples are from a report by George W. Tillson, 
Engineer of the Borough of Brooklyn, New York City, presented at 
the Third International Road Congress in London in 1913.* 

Wood-blocks treated by the creo-resinate process (§ 1158) were 
laid on Tremont Street, Boston, in 1900; and after the pavement 
" had been in use 12 years it had cost absolutely nothing for repairs, 
and was said to be in such a condition that it would probably remain 
intact for 10 years longer. It is stated by the engineer in charge of 
the Boston pavements that the same is true of 14,000 square yards 
laid at about the same time and in the same way." 

" In the Borough of Brooklyn, the first creosoted wood pave- 
ment was laid in 1902, without any guarantee, and has cost abso- 
lutely nothing for repairs. Pavements that were laid later and have 
been out of guarantee from 3 to 4 years, have been kept in repair by 
the Borough; and an accurate record kept of their cost. Some of 
these pavements have cost absolutely nothing, and the average cost 
for the entire area out of guarantee has been 1.05 cents per square 
yard per year. Many of these pavements, however, have been 
opened for sub-surface work; and the engineer in charge of pave- 
ments states that in his opinion practically all of the repairs are due 
to settlements over trenches and damage caused by fires, and not to 
actual wear and tear of traffic." 

'' The Borough of Manhattan has three streets which have been 
out of guarantee three years, one of heavy traffic, one of medium 
traffic, and one of light traffic. The heavy traffic street has cost 7 
cents per square yard per year, while the average of all has been 
6 cents per square yard per year. But the repairs have been due to 
wear and tear only on the heavy traffic street, which is a wholesale 
street in the business section. Repairs on the other streets are due to 
settlements over trenches, and damage caused by fire; and prac- 
tically nothing to wear and tear of traffic." 

* Engineering and Contracting, Vol. 40 (1913), p. 7-9. 



632 WOOD-BLOCK PAVEMENTS [CHAP. XIX 

'' The City of Minneapolis, Minn., has 1,000,000 square yards of 
wood-block pavements, the first of which was laid in 1902. The 
City Engineer states that these pavements have required practically 
no repairs, the cost in 1911 being less than -ru cent per square yard. 
He also states (in 1913) that the street paved in 1902 is in good con- 
dition, and looks as if it might last for 10 years longer." 

" In St, Louis, Mo., in 1909, the repairs to 50,000 square yards 
of wood pavement laid in 1903 cost $2.10; and in 1911 these same 
50,000 square yards cost less than -^ cent per square yard, so that 
the total cost of repairing the 50,000 square yards of wood pavement 
the first nine years they were laid was -ro cent per square yard. 
These pavements are all on light traffic streets." 



CHAPTER XX 
SELECTING THE BEST PAVEMENT 

1217. KiNDvS OF PAVEMENTS. Pavements have been con- 
structed of a variety of materials; but the forms discussed in the 
preceding chapters — hydrauHc concrete, bituminous concrete, asphalt, 
brick, stone block, and wood block — are the only ones of importance 
now constructed ; and it is improbable that any other paving material 
of value will be introduced. From time to time notices appear in 
the general newspapers of the introduction of some new pavement. 
Among the new paving materials of which somewhat laudatory 
notices have appeared are compressed hay, devitrified glass, cork, and 
rubber. All such novelties are either an attempt of an eccentric 
inventor to sell his goods, or a construction to meet Umited and 
peculiar conditions. For example, it has been stated that rubber 
has been tried as a paving material in London ; but the facts are that 
it has been used only to the extent of 300 or 400 square feet in a hotel 
porte cochere. 

1218. Table 75, page 634, shows the number of miles and the 
percentages of the different kinds of pavements in the 158 cities 
having a population of over 30,000 in 1909. These data are the same 
as those in the table on page 320. 

It is interesting to note that (1) practically one half of all the 
pavements in Table 75 are in the 16 cities having a population of 
300,000 or over ; (2) two thirds of the asphalt pavements are in cities 
having a population of 300,000 or over, and that one third of this 
amount is in New York City; (3) New York City, Indianapolis and 
Minneapolis have more than one half of the creosoted wood-block 
pavements ; and (4) nearly one half of the water-bound macadam is 
in cities having a population of over 300,000. 

Table 76, page 635, shows the percentages of the different kinds 
of pavements for three different dates in the larger cities of the 
United States. These data are interesting as showing the progressive 

633 



634 



SELECTING THE BEST PAVEMENT 



[chap. XX 



TABLE 75 
Percentages of Different Kinds of Pavements* 
In 1909 in cities having a population of 30,000 or over 



Ref. 

No. 


Kinds of Pavement. 


Length, Miles. 


Per Cent. 


1 


Asphalt-sheet 


4 293 
261 
192 

2 807 

536^ 

25 

2 556 
274 

6 325 

142 

16 

2 596 
156 . 
6142 
211 


20 4 


2 
3 


block 

Bitulithic . 


1.2 
9 


4 


Brick 


13 4 


5 


Cobble stone 


2 6 


6 

7 


Concrete — portland cement 

Gravel — water-bound 


0.1 
12 2 


8 


bituminous-bound 


1 3 


9 


Macadam — water-bound 


30 1 


10 


tar-bound 


00 7 


11 


portland-cement grouted 

Stone block 


0.08 
12 4 


13 
14 
15 


Wood block — creosoted 

untreated 

Other kinds 


0.7 
2.9 
1 




Total 






21004 


100 









Nearly half in Baltimore. 



2 More than half in Chicago. 



changes in the percentages of the different forms of pavements. 
For example, note the increase in the percentage of asphalt pave- 
ments, and the decrease in cobble-stone. Notice that no brick pave- 
ments were reported separately in 1890. It is interesting to note 
that the percentages of water-bound macadam and stone-block 
pavements, the extremes as to durability, remained nearly stationary. 
The increase in the total number of miles of pavements, is shown 
below. 



Year. 


Number of Cities. 


Cities Having Popu- 
lation OF Over. 


Total Miles of 
Pavement. 


1890 
1901 
1909 


262 
135 
158 


10 000 
30 000 
30 000 


12 453 
15 099 
21004 



Doubtless if Table 76 were brought up to date, there would 
be some material changes. For example, cobble-stone pavements 
would practically disappear, portland-cement concrete would greatly 
increase, bituminous concrete (other than bituHthic) would appear 
in the list, a considerable proportion of the water-bound gravel and 
macadam pavements would change to bituminous bound, and un- 
treated wood block would nearly disappear. 

* Compiled from "General Statistics of Cities for 1909," Bureau of Census, Washington. 
D. C, 1913, p. 154-59. 



ART. 1] 



THE DATA FOR THE PROBLEM 



635 



TABLE 76 
Percentages of Different Kinds of Pavements at Different Dates 



Ref. 

No. 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 



Kind of Pavement. 



Percentages in 



1890' 



19012 



1909 3 



Asphalt-sheet 

block 

Bitulithic 

Brick 

Cobble-stone 

Concrete — portland cement 

Gravel — water-bound 

bituminous-bound 

Macadam — water-bound 

tar-bound 

portland-cement grouted. 

Stone block 

Wood-block — creosoted 

untreated 

Other kinds 



3.2 



15.1 
31.0 



27.0 



12.1 



7.8 
2.9 



Total 



100.0 



13.6 



"7.9" 

6.8 


■■14.7" 


■'30.6" 


"i3:4" 



8.7 
4.3 



100.0 



21.6 

0.9 

13.4 
2.6 
0.1 

12.2 
1.3 

30.1 
0.7 
0.08 

12.4 
0.7 
2.9 
1.0 



100.0 



1 Compiled from "Social Statistics of Cities, Eleventh U. S. Census, 1890," p. 15-16. 

2 Compiled from "Statistics of Cities, Bull. No. 36, U. S. Dept. of Labor, Sept., 1910," 
p. 876-79. 

3 Compiled from "General Statistics of Cities for 1909," U. S. Bureau of Census, Washing- 
ton, D. C, 1913, p. 154-55. 



Art. 1. The Data for the Problem 

1219. Durability of Pavements. The durability or life of a 

pavement is the most important factor in determining which is the 
best pavement. The durability of a perishable paving material, as 
untreated wood and to some extent macadam and asphalt, depends 
upon both the climate and the traffic; but in general the durability 
of paving materials depends chiefly upon the amount of the travel, 
and consequently the durability of different pavements can be accu- 
rately compared only when the nature and the amount of the travel 
over each is known. Unfortunately there are very little definite 
data as to the amount of travel upon American pavements. Not 
infrequently the travel on a particular pavement is referred to as 
being " heavy " or " light," but such general terms are practically 
worthless in comparing the durability of different kinds of pavements. 

1220. Travel Census. Although data on the use made of pave- 
ments are of vital importance in attempting to compare the relative 
durability of different paving materials, comparatively few obser- 
vations have been made concerning the travel upon American pave- 



636 



SELECTING THE BEST PAVEMENT 



CHAP. XX 



ments. For a discussion of the causes that have led to this surprising 
result, see § 640-42 (page 321-24). For a statement of the im- 
portance of a travel census in considering the cost of construction 
and maintaining a road or pavement, see § 29 (page 25) . For a brief 
accoimt of some observations made concerning the nature and 
amoimt of the travel on rural roads, see § 30-33 (page 26-28) ; and 
for a brief reference to the few censuses that have been taken of travel 
on American streets, see § 34 (page 28). 

In some respects the most elaborate census of street travel taken 
in this country was that made by the Barber Asphalt Paving Com- 
pany in 1885. Table 77, page 637, shows the results. It is not worth 
while to describe the methods employed in making the observations 
or in computing the results, since the data are very greatly out of 
date owing to radical changes in both the character and the amount 
of the travel. For example, in St. Louis from 1914 to 1915, the total 
travel on certain business streets increased 20 per cent, the motor- 
driven traffic increasing 53 per cent and the horse-drawn decreasing 
15 per cent.* However, apparently the data in Table 77 are the 
most elaborate that have yet been published. Table 77 is instruc- 
tive as showing the great variation in the travel on different streets 
of any particular city and also of different cities. 

1221. Table 78, page 638, gives the travel record of certain streets 
in London and Liverpool. The marked difference in the travel on 
the pavements of London and on those of New York is due chiefly 
to the use of omnibuses in London and street cars in New York City. 
This example illustrates the importance of having definite data as 
to the amount of travel; and also shows the importance of taking 
account of local conditions in attempting to compare the results in 
one city with those in another. 

1222. It is desirable that engineers in charge of streets should 
ascertain by direct observation the amount of tonnage passing over 
each pavement, in order that the service per unit of cost of different 
pavements may be accurately compared. The only measure of the 
durability of a pavement is the amount of travel tonnage it will bear 
before it becomes so worn that the cost of replacing it is less than the 
expense incurred by its use. It is also desirable that all such observa- 
tions should be made in accordance with a standard plan, so the 
results from different cities will be comparable (see § 35-38). 

1223. Elements Modifying Durability. Although the effect of 



* Engineering News, Vol. 76, (1916), p. 832-34. 



ART. 1] 



THE DATA FOR THE PROBLEM 



637 



TABLE 11 
Travel on Certain Streets in Various American Cities in 1885* 



Locality. 



City. 



New York 



Philadelphia 







Boston. . . . 

n 
u 




11 
u 




u 


St. 

it 


Louis... 


ii 


u 


u 


ii 


li 


ii 



New Orleans 



Washington 



Buffalo. 



Louisville. 



Omaha. 



Street. 



Broadway, near Pine 

Fifth Ave., opp. Worth Monum't. 
Wail, corner of Broad 



Broad, in front of P.R.R. Station 
Filbert, in front of City Hall. . . . 
Chestnut, corner of Fourth 



Wabash, near Lake 

Clark, near Madison 

La Salle, near Locust 

Dearborn, opp. Washington P'k . 

Devonshire, opp. Post Office . . . . 

Devonshire, near Milk 

Kilby, near State 

Washington 

Arch, near Summer 

Court Square 



Locust, near Beaumont . . 
Broadway, near Olive. . . . 

Pine, near Garrison 

Chestnut, near Beaumont 
Olive, near Beaumont. . . . 



Tchoupitoulas, near Poydras. 
St. Charles, near Washington 

15th, opposite Treasury 

9th, between D and E 

7th, between D and E 

6th, between Pa. Ave. and B. 



Main, near Swan 

Main, near Bouck Ave. 
Linwood, near Ferry. . . 
Main, near Glenwood. . 



Main, near 3d. . . . . 
8th, near Walnut. . 
7th, near Jefferson. 



Douglass, near 15th. 
Farnham, near 14th 



40 
40 

27 

65 
65 
26 

50 
45 

36 

38 

27 
32 
26 
39 
26 
24 

36 
50 
36 
36 
36 

40 
30 

70 
50 
50 
60 

56 
42 

38 
50 

61 
36 
35 

63 
60 



Number of Tons. 



Total 
per Day. 



10 905 
3 744 
2 357 

9 237 

6 302 
1928 

7 561 
6 398 
2 756 

2 604 

5 301 

5 028 

3 265 

2 938 

1 130 
744 

3 691 

3 618 

2 554 
942 
259 

6 204 
1065 

4 622 

1688 
1455 
1289 

2 613 
1505 

825 
714 

4 176 

2 402 

977 

2 967 
1 449 



Per 

Vehicle. 



1.39 

.68 

1.00 

1.52 
1.24 
1.06 

2.08 

1.46 

.90 

1.11 

.99 

1.02 

.93 

.80 
.79 
.67 

1.13 

1.23 

1.16 

.90 

.84 

1.81 
.94 

1.02 

.87 

.88 

1.01 

.83 
1.88 
1.47 
1.24 

1.25 
1.05 
1.05 

.62 

.59 



O 43 >i 

!-; o a 



273 
94 

87 

142 
97 

74 

151 
142 

77 
69 

196 

157 

126 

75 

43 

32 

103 

72 
70 

27 
7 

155 
35 

66 
34 
29 
21 

47 
36 
22 
14 

69 

67 

28 

47 
24 



* Trana. Aaier. Soc. of Civil Engrs., Vol. 15 (1886), p. 123-38. 



638 



SELECTING THE BEST PAVEMENT 



[CHAP. XX 



TABLE 78 
Travel on Certain Streets in London and Liverpool in 1879* 



Ref. 

No. 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 
19 
20 
21 



Locality. 



City. 



London 



Liverpool 



Street. 



Gracechurch. . . . 
King William . . , 

Poultry 

Strand and Fleet 

Parliament 

Oxford 

Cheapside 

Leadenhall 

Piccadilly 

Euston 

Brompton 

King William . . . 
Edge ware. . . . . . 

Regent 

King's 

Victoria 

Sloane 

(Not named) . . . 

Great Howard . . 
Bold 



Pavement. 



Kind. 



Asphalt 

Wood 

Asphalt 

Wood 

Macadam 

Wood 

Asphalt 

(I 

Macadam 

Granite 

Wood 

Granite 

a 

Macadam 
Wood 

Macadam 
Wood 

Granite 

u 

Wood 



32 
40 
22 
37 
45 
57 
32 
30 
37 
44 



32 
43 
52 



.40 



Number of Tons. 



Per Day. 



13 507 

16 484 

8 330 

13 596 

14 380 

17 076 

9 260 
7 588 
9 358 

10 658 



6 506 

8 376 

9 668 



5 780 



Per 
Vehicle. 



1.11 

1.06 
1.02 

.84 
1.01 
1.01 

.98 
1.08 

.87 
.88 



1.02 

1.02 

.90 



96 



■4-. O 

Oh 



422 
412 
378 
367 
322 
300 
290 
253 
253 
242 
216 
203 
195 
186 
156 
145 
93 

382 
232 
231 
100 



travel is dependent chiefly upon the number of tons per foot of width, 
its influence is modified somewhat by (1) the character of the pave- 
ment, (2) the state of repairs, (3) the degree of cleanhness, (4) the 
presence or absence of car tracks, (5) the width of pavement, (6) 
the character of the travel, and (7) the climate. 

1. The durability of a particular kind of pavement will vary 
with the details of the method of construction. The foundation 
may be more or less rigid, the materials may differ greatly in dura- 
bility, with any form of block pavement the joints may be more or 
less open, and the surface may also vary more or less in roughness. 

2. The durability will depend upon the care employed in repairing 
the pavement. If holes, depressions, or ruts are aflowed to remain 
for any length of time, whatever the material the pavement wiU 
wear abnormally fast. 

3. The degree of cleanness will materially modify the durability 



* Trans, Amer, Soc, of Civil Eng'rs, Vol. 15, (1886), p. 131. 



ART. 1] THE DATA FOR THE PROBLEM 639 

of a pavement. An imperishable material is benefited by a cov- 
ering of detritus, since it serves as a carpet to protect the pave- 
ment; and if the covering is heavy enough, the pavement virtually 
becomes a foundation and is entirely protected from wear. On the 
other hand, the decay of a perishable material, as wood and asphalt, 
is hastened by a covering of street dirt which collects moisture and 
hastens the decay and disintegration of the pavement. 

4. The presence of a street-car track on a street concentrates 
traffic at the two sides, thus virtually narrowing the street, and also 
causes the travel to go substantially in one track, a result which 
is particularly destructive of gravel and macadam roads. 

5. The wider a pavement the more evenly will it wear, and conse- 
quently the longer it will last. If several irregular lines of travel can 
be maintained, the wear will be much more even and the durability 
greater than if the vehicles are restricted to practically a single line. 

6. The durability of the pavement will vary with the weight per 
unit width of tire, the method of shoeing the horses, and the rapidity 
of the travel. In Europe, the weight per unit of width of tire is 
generally regulated by law, and calks on the horses' shoes are pro- 
hibited ; but in America there are no such restrictions. Rapid travel 
is more destructive to a block pavement than slow travel. 

7. The climate affects the durabihty of several kinds of pave- 
ment. The durability of an untreated wood pavement is affected by 
heat and moisture conditions, that of macadam and gravel by mois- 
ture and winds, and that of asphalt by moisture, particularly by 
street sprinkling. 

1224. There are two facts of a somewhat different character 
that should not be overlooked in attempting to determine the life of 
a pavement. 

1. The average wear does not determine the life of a pavement, 
since even the most carefully constructed pavements wear so unevenly 
as to require re-laying before the wearing coat is entirely worn out. 
This is true of sheet asphalt and gravel and macadam (both water- 
bound and bituminous), which have a comparatively thin wearing 
coat; and is particularly true of pavements made of blocks, as brick, 
stone and wood, since the edges of the blocks wear off and leave 
the top face rounded, and when the pavement reaches this stage the 
wear is much more rapid than previously. 

2. In a block pavement the blocks must have a certain depth to 
enable them to keep their place; and consequently bricks and shallow 
wood blocks can not be worn more than about half-way through. 



640 



SE:LECTING THE BlJST PAVEMENT 



[chap. XX 



If the blocks are made deeper, the durabihty of the pavement is 
not increased much, if any, since owing to unequal wear the pave- 
ment must be re-laid before any considerable depth is worn off. 

Asphalt and macadam have some decided economic advantages 
over other forms of pavements, since the wearing coat is compara- 
tively thin and can be replaced when it is worn out or wears rough, 
without proportionally as much loss as when a block pavement is re- 
surfaced. A further economic advantage of these pavements is 
that when holes begin to form, a patch may be appHed and thus the 
uniformity of the surface may be preserved and the Hfe of the pave- 
ment be extended. 

1225. Data on Life of Pavements. Until more complete data 
concerning the volume of travel on pavements and the amount of 
wear are obtained, it will be impossible to make any reliable estimates 
as to the durability of different paving materials. At present the 
best that can be done is to accept the estimate of those most com- 
petent to give an intelligent opinion. 

1226. Asphalt, Brick, and Wood. Table 79 gives the estimated 
life of sheet asphalt, brick, and wood-block pavements as reported 
to the U. S. Census Bureau. An extensive list was given for asphalt 



TABLE 79 
Estimated Life of Pavements* 



Ref. 

No. 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 



City. 



New York City, N. Y. 

Boston, Mass 

Cleveland, O 

Indianapolis, Ind 

Portland, Ore 

Columbus, Ohio 

Toledo, Ohio 

Atlanta, Ga 

Oakland, Calif 

Cambridge, Mass 

Springfield, Mass 

Holyoke, Mass 

South Bend, Ind 

Saginaw, Mich . 

Sacramento, Calif. . . . 
Galveston, Tex 



Sheet Asphalt 






12 
10 



10 
5 
11 
10 
11 
15 
12 
12 
10 
10 
18 
12 
7 



T3 23 

Pi 



15 
15 
14 
12 
10 
14 
20 
14 
25 



10 
15 
18 
20 
10 



Brick. 



_^^ 






l-g 






e 2 


T3.2 


§Q 


IQ 


« 


« 


11 


11 


5 


10 




25 


10 


25 


18 


18 


10 


25 


12 


25 


12 


12 


15 


18 


15 




20 


25 


12 


20 



11 



11 



Wood 


-BLOCK. 


+^ 


a -t^ 






M 'C 


C"C 




4) +j 


C.2 


-c.S 


§Q 


■fQ 


PQ 


tf 


15 


20 


11 






20 


9 




13 






30 



17 
15 
10 
.10 

8 



30 
25 
15 



18 



15 
30 

20 



* General Statistics of Cities for 1909, Bureau of the Census, 1913, Washington, D. C. 



p. 69-70. 



I/V 



ART. 1] THE DATA FOR THE PROBLEM 641 

and brick, but only a brief list for wood-block; and only those in 
the former list are presented in Table 79, for which data were 
given also for wood-block. 

Of course, the life of a pavement will depend upon the specifica- 
tions and the details of the construction, which can not be pre- 
sented in a tabular statement. Further, the Hfe of a pavement 
depends upon the extent and character of the annual repairs. It is 
possible to keep some types of pavements, as for example sheet 
asphalt, going almost perpetually by patching; while with other 
forms, as for example brick, it is not possible to greatly prolong the 
life of the pavement by patching. 

1227. Granite. The census report from which the data in Table 
79 were taken, contained no statistics for the life of stone-block pave- 
ments. The following data to some degree supply that lack. 

Mr. Samuel "WTiinery, a competent authority, estimates the life 
of granite-block pavements in Boston as follows: * 

A, central business streets having a very large volume of the heaviest 

travel 13 years 

B, secondary business streets with travel of moderate volume and weight . 17 years 

C, main city or suburban thoroughfares having a large volume of com- 

paratively light travel 16 ^^ 

D, suburban or residence streets where the travel is mainly of a local 

character and light 20 " 

Mr. George W. Tillson, Consulting Engineer, Borough of Brook- 
lyn, estimates the life of a granite-block pavement at 25 years. f 

The Bureau of Municipal Research of Cincinnati, Ohio, estimates 
the hfe of granite blocks at 25 years, t 

1228. Water-hound Macadam. Macadam varies in quality more 
widely than any of the preceding forms of pavements, and hence 
there is a wider range in its estimated hfe. 

Mr. Whinery estimates the hfe of trap-rock water-bound mac- 
adam for the four classes of streets mentioned in the second para- 
graph of § 1227, as follows: 

A, 5 years; B, 6 years; C, 7 years; and D, 10 years. 

The Bureau of Municipal Research of Cincinnati estimates the 
life of limestone water-bound macadam at 8 years. J 

* Report to the Finance Committee of Boston, Mass., Engineering and Contracting, Vol. 73 
(1910). p. 30-31. 

t Paper presented to International Municipal Congress, Chicago, Engineering and Con- 
racting. Vol. 36 (1911), p. 405. 

J Municipal Engineering, Vol. 42 (1912), p. 459. 



642 SELECTING THE BEST PAVEMENT [CHAP. XX 

1229. Requirements of an Ideal Pavement. The perfect 
pavement is an ideal which will never be attained, since some of 
the qualities required in a perfect pavement are antagonistic to 
each other. For instance, perfect durability would require a pave- 
ment without friction, for friction causes wear and ultimately destruc- 
tion of the pavement; but without friction there could be no adequate 
foothold for horses drawing loads. Again, to be the least injurious 
to horses, a pavement should be soft and yielding; but a soft and 
yielding pavement is opposed to ease of traction. The conditions to 
be fulfilled by the ideal pavement will first be considered; and sub- 
sequently an attempt will be made to estimate the degree to which 
each kind of pavement approximates the perfect ideal. 

A perfect pavement should satisfy the following conditions: 

1. It should be low in first cost. 

2. It should be durable, i. e., the cost of perpetually maintaining 
its surface in good condition should be small. 

3. It should have a smooth, hard surface, so as to have a low 
tractive resistance. 

4. It should afford a good foothold to enable horses to draw 
heavy loads, and to prevent them from slipping and falling and 
possibly injuring themselves and blocking traffic. 

5. It should be smooth, so as to be easily cleaned. 

6. It should be comparatively noiseless. 

7. It should be impervious, so as to keep in good sanitary condition. 

8. It should yield neither dust nor mud. 

9. It should be comfortable to those who ride over it. 

10. It should not absorb heat excessively. 

Each of the ordinary forms of pavements will be considered under 
each of the above requirements. 

1230. Cost of Construction. The cost of construction of a pave- 
ment varies with the specifications, the character of the work, and 
the locality. For detailed data on this subject, see the several kinds 
of pavements in the preceding chapters. 

Since the subject under consideration in this chapter is a com- 
parison of the different forms of wearing coats, the cost to be con- 
sidered here is that of the pavement exclusive of the expense for 
curbs, gutters, catch-basins, etc. To have data for use in sample 
computations later in this chapter, the cost of the best grade of each 
of the several kinds of pavements is assumed to be as follows: 

1. Asphalt, sheet $1 .75 per sq. yd. 

2. Brick 1 .80 " '' " 



ART. 1] THE DATA FOR THE PROBLEM 643 

3. Granite block 3.00 per sq. yd. 

4. Macadam, water-bound 1-25 

5. Wood block, creosoted 2 . 75 

1231. Cost of Maintenance. By the cost of maintenance is 
meant the expenditure necessary to keep the pavement in practically 
as good a condition as when it was new. Unfortunately there is a 
greater dearth of exact information under this head than for almost 
any other phase of pavement construction. For a general state- 
ment of the causes of this lack, see § 640^3 (page 321-26) ; and for a 
more detailed explanation why there is Uttle accurate information 
on the cost of repairs of asphalt pavements, which reasons substan- 
tially apply also to all kinds of pavements, see § 881-82 (page 455-57). 

The cost of maintenance consists of two distinct elements, viz.: 
(1) the cost of repairing or patching of small areas; and (2) the cost 
of renewing or re-surfacing large areas. Each will be considered 
separately. 

1232. Cost of Repairs. The cost of repairs is here used as mean- 
ing the cost of correcting any defects that may have developed 
through use. Not infrequently this term is used to include also the 
expense of re-laying or restoring the surface of the pavement after 
it has been opened to lay or repair sewers, water or gas pipes, etc. 
In one sense the cost of restoring the surface after the pavement has 
been opened is part of the cost of maintenance; but the cost of 
restoring the surface is practically independent of the quality or life 
of the pavement, and hence should not be included in comparing the 
economic value of the different pavements. 

Unfortunately, not many municipalities keep accurate accounts 
of the cost of repairing and restoring pavements, and very few 
separate the costs of patching and restoring; and hence there are 
almost no reliable data on the cost of repairs. 

Further, many of the accounts purporting to show the cost of 
repairs contain one or both of the two serious errors discussed in the 
two succeeding sections. 

1233. Repairs vs. New Construction. In computing the cost 
of repairs of roads and pavements, it is common to fail to discrim- 
inate between the renewal of an old surface and the substitution 
of a new and better surface; or, in other words, it is common to 
charge to maintenance an item which should be charged to new 
construction (see paragraph 6, § 881, page 455). For example, if 
some form of bituminous wearing coat is applied to an old water- 
bound macadam road, the new surface is not a renewal of the old one, 



644 SELECTING THE BEST PAVEMENT [cHAP. XX 

but is the construction of a new pavement surface upon the old one 
as a foundation; and consequently the cost of the new construction 
should not be regarded as the cost of repairs to the old pavement. 
This mistake in almost the exact form of the above example has 
often been made in discussions of highway economics. For example, 
it is often stated that the cost of road maintenance has recently 
taken an enormous leap upward due to the advent of the automo- 
bile; while the truth is that the advent of the automobile has caused 
the substitution of a more expensive form of road construction, and 
httle or nothing is known as to the cost of maintenance of the new 
form of construction, partly because the methods of both construc- 
tion and maintenance have been experimental, and partly because 
not enough time has elapsed to secure trustworthy data. 

Because of the above error, many estimates of the cost of 
annual repairs are radically wrong, as also the resulting conclusions. 
Errors of this character have for somewhat obvious reasons been 
more common in connection with surfaces suitable for light travel 
than for heavy travel. 

1234. Age of Pavement. Sometimes an error is made by not 
duly considering the age of the pavement. During the first part of 
the life of a pavement, there should be but few, if any, repairs; 
and hence to secure a trustworthy value for the annual cost of repairs, 
an average should be taken for a number of years, the exact number 
being proportional to the life of each particular pavement. 

Obviously, the greater the area of the pavements included and 
the greater the number of years the better; but it is not correct to 
simply take an average of the annual cost of repairs for each of sev- 
eral pavements of different ages and areas. Assume that the areas 
and ages of the several pavements are as below; that the total cost 
of repairs for each pavement is known ; and that the correct average 
annual cost of repairs is desired.* 



Area, Sq. Yd. 


Age 


, Years. 


Yards XYears. 


10 000 




16 


160 000 


8 000 




12 


96 000 


7 000 




10 


70 000 


8 000 




8 


64 000 



33 000 390 000 

Multiplying the area by the corresponding age gives the number 
of yard-years that have been repaired, i. e., gives the equivalent of 

* Engineering and Contracting, Vol. 37 (1912), p. 311. 



ART. 1] 



THE DATA FOR THE PROBLEM 



645 



the number of yards that have been maintained for 1 year. The 
total cost of repairs divided by the total yard-years (390,000) will 
give the correct average annual cost of repairs. The weighted average 
age of the pavement in the above example is: 390,000 -^ 33,000 = 
11.8 years. 

1235. Data on Cost of Repairs. For a few data on the cost 
of the different kinds of pavements, see the preceding pages, as 
follows: Sheet asphalt. Table 47, page 457, and Fig. 162, page 459; 
brick, § 1069, page 564; wood block, § 1214, page 631. 

Table 80 shows the best general data available, although it is 
not certain that these values, or the ones referred to in the paragraph 
above, are free from the two errors mentioned in the two pre- 
ceding sections. Table 80 is given primarily to have data for use in 
sample computations to be presented later. 



TABLE 80 

Assumed Average Annual Cost of Repairs 





Cents per Sq. Yd. per Annum. 


Kind of Pavement. 


Heavy Travel. 


Light Travel. 


Asnhalt sheet — see § 886 


5.0 
3.0 
10.0 
2.0 
4.0 


3 5 


Brick,— see § 1069 

Macadam water-bound 


2.0 

2 0* 


Stone block,— see § 1142 

Wood block, creosoted, — see § 1214 


2.0 
2.0 



1236. Cost of Renewal. The second element in the cost of main- 
tenance of a pavement is the cost of renewal. Since the foundation 
or base of a modern pavement is not subjected to wear or disinte- 
gration, the cost of renewal is only the cost of adding a new wearing 
coat; although, not infrequently, the cost of a new concrete base is 
erroneously included in the cost of renewal (see § 1233). 

The annual cost of renewal is that sum which each year must be 
placed at compound interest to accumulate a sum equal to the esti- 
mated cost of renewal at the end of the life of the wearing coat of the 
pavement. As an example, it will be assumed that the cost of 
renewal is desired for a sheet asphalt pavement. It will be assumed 
that the pavement costs $1.75 per square yard (§ 1230), and that the 
grading and concrete base cost $1.00 and the wearing coat $0.75. 
The latter is a little less than the pro rata share according to Table 45, 

* Report Dept. of Public Works, Bureau of Engineering, Buffalo, N. Y., 1915-16, p. 70. 



646 SELECTING THE BEST PAVEMENT [CHAP. XX 

page 453; but round numbers are sufficient for an example. The 
life of the wearing coat will be taken as 15 years, which is probably 
too small, notwithstanding the data in Table 79, page 640. It will 
be assumed that the life of the concrete base is 30 years, which is 
probably too small ; and that its removal will cost 20 cents per square 
yard. Interest will be assumed at 3J per cent. It will be further 
assumed that the removal of the old wearing coat wiU cost 10 cents 
per square yard. Finally, to find the annual sum to be placed at 
interest, a sinking fund table is desirable. 

From a sinking-fund table it is found that $0.05182 deposited 
annually at 3 J per cent interest will amount to $1.00 in 15 years; 
and that at the same interest $0.01937 will amount to $1.00 in 30 
years. Then the annual cost of renewal is as follows : 

r^„^. Annual Cost 

I'^^^- Cts. per Sq. Yd. 

Concrete base: renewal, $0.75 X 0.01937 1 .452 

removal, 20 cents -^ 30 0.667 

Wearing coat: renewal, $1.00 X 0.05182 5 . 182 

removal, 10 cents -^ 15 . 667 



Total 7.968 

In some cases there is a salvage value to the old wearing coat, in 
which case its value after removal divided by the Hfe of the pave- 
ment should be subtracted from the annual cost found as above. 

1237. Economic Life of a Pavement When does the cost of 
repairs become great enough to justify renewal, that is, what is the 
economic life of a pavement? This subject has frequently been dis- 
cussed by writers on road and pavement economics, and generally 
the method employed has been radically wrong. For an elaborate, 
correct, and instructive discussion of this subject, see Gillette's 
Hand-book of Cost Data, Second Edition, page 27-34. 

1238. Tractive Resistance. Table 8, page 21, gives the tractive 
resistance of different pavements, from which it is seen that the 
rank of the various pavements according to tractive resistance, in 
order beginning with the one offering the least resistance, is about as 
follows : portland-concrete, sheet asphalt during cold weather, brick, 
best water-bound macadam, asphalt during warm weather, rectan- 
gular wood block, good gravel, accurately dressed stone block, 
ordinary water-bound macadam, gravel, roughly dressed stone block. 
The tractive resistance will vary greatly with the state of repair of 
the surface. 

Many attempts have been made to compute the financial advan- 



ART. 1] 



THE DATA FOR THE PROBLEM 



647 



tage of a decreased tractive resistance; but it is impossible to deter- 
mine its value with any degree of accuracy, although it is certain 
that the tractive resistance of the pavements of a city are impor- 
tant factors in determining the cost of conducting transportation. 
Ease of traction is, however, not relatively as important for city 
pavements as for country roads, since in the latter ease of traction 
is a matter of first importance (see § 4-7), while in the former it is 
com.paratively unimportant (see § 634). On the other hand, the 
cost of transportation per ton-mile is considerably more in the cities 
than in the country. 

1239. Slipperiness. The method of comparing pavements in 
this respect is to determine the distance a horse travels on the dif- 
ferent pavements before he falls. The most complete observations 
made in the United States to ascertain the prevalence of accidents on 
the different pavements were made under the direction of Capt. 
F. V. Greene.* The observations were made from 7 a.m. to 7 p.m. 
on six consecutive days in October and November, 1885, in ten of the 
leading American cities on thirty-three streets having the heaviest 
travel for each kind of pavement in the particular city. The number 
of horses observed on sheet asphalt pavement were 360,254, on old- 
style granite block 376,384, and on wood 70,914; and the number 
of miles traveled by the horses while under observation was 41,427 
on the asphalt pavements, 34,723 on the granite, and 4,901 on the 
wood. A summary of the results is shown in Table 81. 

TABLE 81 
Miles Traveled by a Horse on American Pavements before an Accident 

Occurs 
Observations made in 1885 



Ref. 
No. 



Kind of Pavement. 



Asphalt, sheet 

Granite block — old style, 
Woodi 



Fall on 
Knees. 



1534 
510 

408 



Fall on 
Haunches. 



2 180 

5 954 
983 



Complete 
Fall. 



1647 

3 472 

4 901 



Accident 
of Any 
Kind. 



583 
413 

272 



^The kind of wood-block is not stated, and apparently it can not now be determined. 

These data are very much out of date, and are not of much value, 
since the character of the prevaiHng forms . of construction has 
materially changed; but nevertheless Table 81 contains the only 



* Trans. Amer. Soc. of Civil Engineers, Vol. 15 (1886), p. 123-28. 



648 SELECTING THE BEST PAVEMENT [CHAP. XX 

definite data on record for American pavements. No observations 
similar to the preceding have been made for brick pavements; but 
it is probable that they are less slippery than asphalt, wood-block, or 
stone-block. It is certain that modern stone-block pavements, i. e., 
those with comparatively small blocks and narrow joints filled with 
bituminous or hydraulic cement, are less slippery than the old-style 
stone-block pavement upon which the observation in Table 81 were 
made. 

1240. The above observations relate to the slipperiness for a 
horse; but slipperiness is nearly as important for an automobile as 
for a horse. However, no systematic observations have been made 
as to the effect of slipperiness of pavements upon automobile 
traffic. 

1241. Conclusion. It is generally conceded that wood-block 
pavements are the most slippery, sheet asphalt next, brick next, and 
then granite. 

1242. Investigation in Progress. In 1916 the State Highway 
Commission of Massachusetts built ten sections of pavements pri- 
marily to determine their relative sfipperiness. Incidentally it is 
expected that the experiment will demonstrate other things of 
interest.* 

The test sections were built on Washington Street, Boston, on a 
4 per cent grade, and each is 500 feet long. The surfaces of the 
several sections are those ordinarily employed for rural and suburban 
roads rather than those used on city streets; and consist of two of tar 
macadam (§ 604), two of asphalt macadam (§ 604), two of tar con- 
crete (§ 604), one of asphalt concrete (§ 604, 891, and 901), one of 
hydraulic concrete (Chap. VII), one of tar and sand (§614), and one 
of Topeka asphalt mixture (§ 897-98). Each of the first three forms 
ojF pavements was laid with a " rough " and a '' smooth " surface. 

The different materials are subject to the same conditions, and 
hence are strictly comparable; and the same materials were used in 
the several sections, and hence the methods of construction are 
strictly comparable. The only noteworthy conclusions that have 
been announced relate to the durability of the several forms of con- 
struction; and no decision has been reached as to the relative slip- 
periness of the different surfaces. 

1243. Ease of Cleaning. The facility with which a pavement 
may be cleaned is an important matter both economically and 

* Engineering News, Vol. 76 (1916), p. 1162. 



ART. 1] THE DATA FOR THE PROBLEM 649 

esthetically. Col. Geo. E. Waring, noted for his service as Street 
Cleaning Commissioner of New York City, in 1896 estimated that 
if all the streets of New York City were paved with asphalt where the 
grades would permit, the cost of street cleaning would be reduced 
from $1,200,000 to $700,000 per 3^ear. At that time New York had 
431 miles of pavement of which 94 were asphalt, and the above annual 
saving is equal to 3 per cent of the cost of laying asphalt pavements 
upon all of the streets not already asphalted. 

Sheet asphalt and hydrauhc concrete pavements are most easily 
cleaned, and next in order are: wood blocks with close joints, asphalt 
blocks, brick with joints filled with hydraulic cement, accurately- 
dressed stone blocks with cement joints, and old-style stone blocks. 

Macadam and gravel are smooth and for this reason are ea,sily 
cleaned; but their surfaces, particularly if water-bound, grind up 
into powder under dense or heavy travel, and for ih'is reason there is 
considerable detritus to be removed, a fact which adds to the expense 
of cleaning. 

1244. Noiselessness. The noise made by travel upon a pave- 
ment has an important effect upon the comfort and health of the 
people using the pavement or living adjacent to it. A quiet pavement 
is particularly desirable adjacent to office buildings, schools, churches, 
hospitals, etc.; and the noise of travel upon a rough pavement 
aggravates, if it does not cause nervous disorders. 

On sheet asphalt and hydraulic concrete, and well-grouted brick, 
the only noise is the sharp click of the horses' shoes; and on asphalt 
block and re-pressed brick filled with tar or grout, there is the click 
of horse's shoes and a slight rumbling of the wheels passing over the 
joints. On well-dressed granite blocks filled with hydraulic cement, 
there is a considerable rumbling due to the passage of heavy steel- 
. tired vehicles; and on the old-style granite block with sand-filled 
joints, there is a deafening roar due both to the rumbhng of the 
wheels and to the blows of the horses' shoes. Upon wood pavements 
the horses' feet produce no noticeable noise; while the wheels make a 
dull rumbling noise, but not loud enough to be seriously objection- 
able. Macadam and gravel are more quiet than wood. 

In order of their freedom from noise, pavements rank about as 
follows: wood-block having the joints filled with tar or grout, 
sheet asphalt, asphalt block, asphalt concrete, hydraulic concrete, 
square-edged brick having grouted joints, re-pressed brick having 
joints filled with tar or grout, accurately dressed stone blocks having 
joints filled with grout, and old-style stone block. Bituminous gravel 



650 SELECTING THE BEST PAVEMENT [CHAP. XX 

and macadam are nearly as quiet as sheet asphalt, and water-boimd 
gravel and macadam are not seriously noisy. However, the freedom 
from noise on any pavement depends greatly upon the care used in 
construction and maintenance. 

1245. Healthfulness. The effect of a pavement upon the health 
of the residents in its locality will depend upon the tendency of the 
materials composing it to decay, and also upon its permeability. 
The healthfulness of a pavement was much more important formerly 
than at present. The form of pavements that were most unhealth- 
ful have gone out of use. These are: cobble-stone and stone-block 
pavements having joints filled with pebbles, cyhndrical wood-blocks 
with sand-filled joints, and stone-block having wide joints filled 
with sand or pebbles. The difference in healthfulness of the best 
modern pavements is negligible. 

1246. Freedom from Dust and Mud. The materials of an 
ideal pavement should not grind up and make dust in dry weather 
or mud in wet weather. The dust and mud not only add to the 
expense of cleaning the pavement, but are a discomfort to those who 
use the pavement and to those who live or do business adjacent to it. 

1247. Comfort in Use. If the pavement is to be used for pleasure 
driving, the comfort of the users must be considered; and therefore 
the pavement should have a smooth surface which is free from dust 
when it is dry and free from mud when it is wet. 

1248. Temperature of Pavements. During hot weather, there 
is frequently complaint that one pavement reflects or radiates more 
heat than another. Observations made in Washington, D. C, when 
the temperature of the air 2 feet above the pavement was 104° F., 
showed the temperature of three pavements to be as follows: sheet 
asphalt 140°, asphalt block 122°, and macadam 118°.* Observa- 
tions in Boston, when the temperature of the air in the shade was 
98° F., gave the temperature of four pavements as follows: wood 
block 124J°, granite block 115°, sheet asphalt 113°, and macadam 
102 J °. The observations are not conclusive as to the relative tem- 
peratures of different pavements, but show that there is no very 
great difference between the several kinds. The temperature of the 
pavement depends upon its color, which varies with the material. 

* Proc. Amer. Soc. Municipal Improvements, Vol. 5, p. 161. 



ART. 2] THE SOLUTION OF THE PROBLEM 651 



Art. 2. The Solution of the Problem 

1250. The problem of selecting the best pavement for any partic- 
ular case is a local one, not only for each city but also for each of the 
various parts into which the city is imperceptibly divided; and 
involves so many elements that the nicest balancing of the relative 
values for each kind of pavement is required to arrive at a correct 
conclusion. 

There are two methods that may be employed in deciding which 
is the best of several pavements. One method assumes that the 
selection should be made up on econo mic grounds alone^ in wliich case 
the best pavement is that for which the total annual expense is a 
minimum. The other method assumes that the decision should be 
based upon other factors beside the economic features. Each of 
these two methods will be considered; and for convenience the first 
will be called a Problem in Economics, and the second a Non-economic 
Problem. 

1251. Problem in Economics. As a problem in economics, 
the selection of the best pavement consists in finding that form of 
pavement, or wearing course, for which the total annual cost is least. 
The annual cost consists of (1) interest on the cost of construction, 
(2) the annual cost of repairs, (3) the annual cost of renewal, (4) 
the annual cost of cleaning, (5) the annual cost of conducting the 
transportation the pavement carries, and (6) the annual cost of 
sprinkling, — when that is necessary. 

The first three items of cost have already been considered in 
Art. 1. The last three items of expense have not been considered; 
but will now be briefly discussed. 

1252. Cost of Cleaning. Some forms of pavements require 
sprinkling for economic maintenance, as for example water-bound 
macadam; and some types require sprinkling for the comfort of the 
users and of those living adjacent to it. 

The cost of cleaning depends upon the amount and character of 
the travel and also upon the smoothness of the pavement, and more 
upon the former than the latter. The difference in cost of cleaning 
the different forms of modern pavements is not great. For example, 
in 1895-97 in New York City it was determined that the relative 
ease of cleaning different pavements was as follows: asphalt, brick 
and rectangular wood-block, each 100; granite block, 150; Belgian 
block, 160; and cobble-stone, 400. But since the date of that inves- 



652 SELECTING THE BEST PAVEMENT [CHAP. XX 

tigation, cobble-stone pavements have been practically eliminated, 
and Belgian blocks nearly so; while the prevaiUng type of con- 
struction of granite-block pavements has changed so that now 
they are practically as smooth as brick pavements. Hence, if the 
cost of cleaning is omitted, it will not materially affect the con- 
clusion as to the relative economic merits of the different pave- 
ments. 

1253. Cost of Transportation. At first thought, it does not ap- 
pear that the cost of conducting the transportation over a pavement 
is part of its annual cost; but really the cost of the transportation is a 
part of the cost of operating the pavement, and hence is a part of its 
annual cost. The cost of construction is usually paid by the abutting 
property holder, and ordinarily he pays also the cost of repairs and 
renewals; the city usually pays the cost of cleaning; and the owners 
of the horses and wagons and of the motor cars pay the cost of trans- 
portation. 

Modern pavements are so nearly alike in the smoothness and 
hardness of their surfaces that there is no material difference in the 
cost of conducting transportation on them. Further, the transpor- 
tation is conducted by so many different parties under so many 
different conditions, that it is practically impossible to determine 
its cost with any degree of accuracy. 

Therefore, for lack of the requisite data, it is necessary to omit 
the cost of transportation from the summary of the annual cost of 
the pavement; but this omission does not materially affect the con- 
clusion as to the most economical pavement. 

1254. Cost of Sprinkling. Water-bound macadam is about 
the only pavement that requires sprinkhng, either for maintenance 
or for the comfort of users of the pavement or of those living adja- 
cent to it. The cost of sprinkhng will vary widely with the local 
conditions — the character and amount of the travel, the cUmate, 
the material of the road surface, the quality of the construction, 
etc. 

Since this form of pavement surface is rapidly going out of use, 
there are no recent data on this subject. Further, such pavements 
are not likely to be constructed to any appreciable extent in the 
future. Therefore, this item will be disregarded. 

1255. Total Annual Cost. The cost of construction is stated in 
§ 1230 (page 642); Table 80 (page 645) shows the cost of repairs; 
and § 1236 (page 645) shows the method of computing the cost of 
renewals, 



ART. 2] 



THE SOLUTION OF THE PROBLEM 



653 



The method of computing the total annual cost of a sheet asphalt 
pavement under heavy travel is as follows: 

Items. ^^^^^^^« <^9^^ 

Cts. per Sq. Yd. 

Interest: concrete base, $1.00 at 3^ per cent 3 . 500 

wearing coat, $0.75 at 3^ per cent 2 . 625 

Repairs (Table 80, page 645) 5.000 

Renewals (see § 1236, page 645) 7.968 

Total interest, repairs, and depreciation 19 . 093 

1256. A Common Error. Not infrequently, in computing the 
annual cost of a pavement, there is added to the above items an 
annual contribution to a sinking fund sufficient to redeem the bonds 
issued to pay for the pavement. This is incorrect, since a bond issue 
is only a means of deferring the payment of the first cost; and it is 
clearly wrong to include both interest on first cost and an annuity 
to pay the first cost. If the bond matures at the end of the fife 
of the pavement, an annuity to redeem the bond is precisely the 
same thing as a depreciation fund to renew the pavement; and 
hence it is clearly an error to include both in the annual cost. 

1257. Comparison of Total Annual Costs. To compare the eco- 
nomic value of different pavements, a computation similar to that in 
§ 1255 should be made for each pavement; and the one showing the 
least annual cost is the most economical. Substantially the above 
method was applied to three forms of pavements and four classes 
of streets in a certain large city, with results in Table 82. * 

TABLE 82 
Annual Cost of Pavements 





Classes of Streets. 


Kind of Pavement. 


A. 


B. 


c. 


D. 


Granite block 


$0,511 
.521 
.669 


$0,372 
.324 
.430 


$0,365 

.283 
.312 


$0 294 


Sheet asphalt 


222 


Water-bound macadam 


151 







Although the error mentioned in § 1233, i. e., not discriminating 
between renewal and new construction, was made in computing the 
cost of repairs of the macadam, the results are sufficiently correct to 
show the method of utilizing such an investigation. The compu- 
tations included a charge for cleaning for each form of pavement, and 



* Engineering and Contracting, Vol. 33 (1910), p. 31. 



654 SELECTING THE BEST PAVEMENT [CHAP. XX 

also an item for sprinkling the macadam. Of the four classes of 
streets, A had the heaviest travel and D the least. The results 
show that for Class A streets, a granite block pavement is most 
economical; for Class B, sheet asphalt; for Class C, sheet asphalt; 
and for Class D, macadam. 

Of course, the value of an investigation similar to that above 
depends upon the values assumed for the life of each of the pave- 
ments, and also upon the value used for the cost of repairs; but unfor- 
tunately there are practically no reliable data for either of these, and 
hence this method is not as exact as its form impHes. For example, 
for any of the four classes of streets in Table 82, the differences in 
the annual costs of the three pavements are so small that the con- 
clusions might be changed by a change in the assumed life of one 
or the other of the pavements. 

1258. Non-Economic Problem. Sometimes the selection of a 
pavement is determined by a single factor, as for example, the 
proximity of one or more paving materials, and sometimes the 
selection can be made from a consideration of only the economic 
features (see § 1251-58) ; but usually the selection requires a careful 
consideration of all the factors involved. The benefits to be derived 
from good pavements are stated in § 634 (page 318-19), from which it 
appears that only two of the eight advantages relate directly to 
economics. The requirements for an ideal pavement are enumer- 
ated in § 1229, from which it appears that only five of the ten items 
concern economics. 

The decision as to which is the best pavement will often be largely 
a matter of judgment; and when this is the case, the engineer should 
reach his conclusion by a series of carefully considered^steps, and not 
by a single haphazard leap. He should weigh all the evidence, and 
not base a decision upon a single item, as is too often the case; nor 
should he adopt the practice of some other locaHty without a careful 
consideration of the local resources and of the needs of the place in 
which the pavement is to be laid, as is frequently done. 

Local conditions should always be considered, and hence it is 
not possible to lay down any fixed rule as to what material makes the 
best pavement; but a careful study of the requirements of the ideal 
pavement and of the qualities of the different kinds of pavements 
will promote an intelligent selection in any particular case. 

1259. Relative Merits of Pavements. It is proposed to compare 
different kinds of pavements by assigning percentages to the different 
qualities of an ideal pavement, and then with this as a guide to assign 



ART. 2] 



THE SOLUTION OF THE PROBLEM 



655 



numerical values to the various qualities of the several kinds of 
pavements. 

The various quahties of a perfect pavement have been discussed 
in § 1229 to § 1248, and these quahties have been grouped in Table 
83 under the three heads: (1) economic qualities, (2) sanitary 
qualities, and (3) acceptability. Opposite each of these qualities 
in the first column of Table 83 is placed a number which is beheved 
to represent the average relative importance of that particular 
quahty on a scale of 100. 



TABLE 83 
Relative Values for the Different Qualities of Various Pavements 





Qualities. 


Percentage Assigned to the Quality. 


Ref. 

No. 


Ideal 
Pave- 
ment. 


Sheet 
Asphalt. 


Brick. 


Granite 
Block. 


Water- 
bound 
Mac- 
adam. 


Wood 
Block. 


1 


Economic qualities: 

Low first cost 


20 
20 
10 

5 
10 


11 

14 
9 
2 

10 


10 

18 
8 
4 
9 


3 
20 

7 
4 
6 


18 
8 
6 
5 
3 


5 


2 

5 


Low cost of repairs 

Ease of traction 


16 
9 


4 


Good foothold 


2 


5 


Ease of cleaning 


9 




Total 






65 

15 
5 


46 

10 
5 


49 

7 
4 


40 

5 
3 


40 

15 

2 


41 


6 


Sanitary qualities: 

Noiselessness 


14 


7 


Healthf ulness 


4 




Total 






20 

10 
3 

2 


15 

10 
3 
1 


11 

9 
1 
1 


8 

8 
1 
1 


17 

2 
3 
2 


18 


8 

9 

10 


Acceptability: 

Free from dust and mud . . . 

Comfortable to use 

Non-absorbent of heat 

Total . ... 


9 
2 

1 




15 
100 


14 

75 


11 

71 


10 

58 


7 
64 


12 




Grand total. 


71 




1 





The most important matter in preparing Table 83 is the assign- 
ment of the numbers for the Ideal Pavement, for the number assigned 
to any one quahty limits the range of the corresponding assignments 
to the different pavements. The assignment of the numbers is 
wholly a matter of judgment, and different individuals will differ 
greatly as to the relative values to be given to each quality; but the 
table is only to show a method whereby the good and the bad qualities 



656 SELECTING THE BEST PAVEMENT [CHAP. XX 

of one kind of pavement may be balanced against those of another 
kind, and a conclusion may be reached, step by step, which repre- 
sents the algebraic sum of the judgment on each item. 

Different values should be assigned to the same quality according 
to the attendant conditions. If the street is in a manufacturing 
district and subject to heavy traffic, ease of traction should be 
assigned a comparatively high value, and noise a very low value. 
For an office district, quietness is the controlling factor, and should 
therefore have a relatively high value. Similarly, for a residence 
district with its light driving, healthfulness and freedom from dirt 
and dust may be the most important element; for a residence dis- 
trict where the property owners can not afford an expensive pavement, 
the first cost may determine the kind of pavement; and on a steep 
grade slipperiness may out-weigh all other conditions in determining 
the kind of pavement to be employed. The application of the 
principles is likely to be complicated by the personal interests of the 
residents or property-holders, since opinions are fikely to differ 
according to whether the point of view is that of a tenant, a resident 
property-holder, or a non-resident property-holder. 

1260. Each quality of a pavement will now be considered, and 
the degree of perfection of this quality possessed by each kind of 
pavement will be indicated by a numerical value. 

1261. First Cost. In § 1230 (page 642) are given assumed values 
for the average cost of construction for the best of each kind of pave- 
ment. These values are repeated below in the order of their cheapness: 

Kind of Pavement. Cost pee Sq. Yd. Relative Weight 

1. Macadam, water-bound $1 . 25 18 

2. Asphalt, sheet 1 . 75 11 

3. Brick 1.80 10 

4. Wood block, creo^oted 2 . 75 5 

5. Granite block 3.00 3 

The last column of the above exhibit shows the relative weights 
assigned to the quality of cheapness. Since macadam is the lowest 
in first cost, it possesses the quality of cheapness in the highest 
degree; and consequently it is given a weight of 18 — nearly the value 
assigned to the ideal pavement in Table 83. The weights assigned 
to this quality decrease from gravel, the cheapest, to granite block, 
the most expensive. The several weights assigned above to low 
first cost are entered opposite this quality in the table. 

1262. The first cost of a pavement not infrequently has undue 
weight in comparing the relative merits of different kinds of pave- 



ART. 2] THE SOLUTION OF THE PROBLEM 657 

ments. The pavement which costs the most to construct is not 
always the most expensive, nor is the one lowest in the first cost 
always the cheapest in the end (see § 1251-57). 

A pavement is sometimes selected because of its low first cost, 
for other than economic reasons. Often the cost of construction is 
charged against the abutting property, while maintenance is paid 
for by the whole city; and the result is that many property owners 
perfer a cheap pavement because they must pay for it, notwithstand- 
ing the fact that the cheaper pavement may cost more for main- 
tenance and be dearer in the long run. Again, the property holders 
are sometimes really unable to pay for the most economical pave- 
ment, and hence a pavement low in first cost is selected as a tem- 
porary expedient. 

1263. Cost of Repairs. Table 80, page 645, contains the best avail- 
able data on the cost of repairs, although they are not very reliable. 
The data for heavy travel are re-arranged and transcribed below : 

Kind of Pavement. 

1. Stone block 

2. Brick 

3. Wood block 

4. Asphalt 

5. Macadam, water-bound 



Cost per 
2.0. 


Sq. 


Yd. 


Relativi 


. Weight 
20 


3.0. 








18 


4.0. 








16 


5.0. 








14 


10.0. 








8 



1264. Ease of Traction. Under this head may be included not 
only the power required to move loads, but also the consequential 
damages to vehicles, since they both vary with the roughness of the 
pavement. From a study of the results in Table 8, page 21, remem- 
bering that the tractive resistance of the best type of several of the 
pavements has decreased since the observation in Table 8 were 
made, the weights are assigned to this quality for the different 
kinds of pavements, as shown in Table 83. 

1265. Foothold. From a study of § 1239, the relative degree of 
slipperiness is stated in numbers and entered in Table 83. If the 
pavement is to be upon a steep grade, this quahty may be a con- 
trolling factor. 

1266. Ease of Cleaning. The relative ease with which certam 
types of pavements may be swept, as determined by the cost of doing 
the work in New York City, is as follows: asphalt, 100; brick, 100; 
rectangular hard-wood blocks, 100; granite blocks, 150; Belgian 
blocks, 160; cobble stones, 400.* For sanitary reasons, New York 

* Street Cleaning in New York City in 1895-97, p. 157 — Supplement to Vol. II. of Municipal 
Affairs. New York, 1898. 



658 SELECTING THE BEST PAVEMENT [CHAP. XX 

City has spent a million dollars a year for the past few years in sub- 
stituting sheet asphalt pavements for stone-block in the congested 
tenement districts, chiefly on account of the greater ease with which 
the asphalt is kept clean. 

The cost of sweeping ordinary stone-block, round wood-block, and 
brick with sand filler usually ranges between 40 and 48 cents per 1,000 
square yards for each sweeping, and sheet asphalt from 30 to 38 
cents, depending upon the thoroughness of doing the work, the fre- 
quency of sweepings, the kind of business in the property adjoining, 
and the amount of the traffic. The relative weight to be assigned 
to this item will vary with the frequency of cleaning. 

The estimated weight to be assigned to the several pavements 
on account of their ease of cleaning is entered in Table 83. 

1267. Value for Other Qualities. From a consideration of the 
discussion in § 1244-48, the percentages for the other quahties are 
inserted in Table 80. 

1268. Conclusion. The totals at the foot of Table 83 represent 
the summation of the individual decisions on the several quahties, 
and the larger the total the more desirable the pavement. The 
particular results in this example may not be appHcable to any 
locality, and each person will have his own opinion as to the merits 
and defects of any particular pavement; but the method of analysis 
is applicable to any particular case, and will enable the engineer 
intelligently and unerringly to reach the final conclusion to which his 
opinion in detail leads. The above method has something of the 
mathematical form ; but the fact should not be forgotten that it is 
based upon judgment, and that therefore it can not be expected to 
give results of a high degree of accuracy. 

In practice the application of this method is much less compli- 
cated than appears from the above example, for usually proximity 
of some natural pavement material or freight rates on others, limits 
the choice to a comparatively few kinds of pavements. Further, the 
decision as to the kind of pavement to be laid is often influenced by 
the fancy or abiUty of those who pay for it. However, the engineer 
should employ a logical process in arriving at his own conclusions, 
and thus be in a position to give sound advice upon the funda- 
mental principles involved. 

1269. Finally, in any important case, it is wise to determine the 
best pavement by both the economic and the non-ecomonic method, 
so as to check one method against the other. 



INDEX 



ASP 

Asphalt, 267 
American, 270 
Bermudez, 269 
California, 269 
cement, 268 

preparation, 274 
specifications, 275 

binder for macadam, 278 
bituminous concrete, 279 
bituminous surface, 277 
filler for block pavements. 282 
seal coat, 280 

sheet asphalt pavements, 281 
characteristics, 268 
cost, 2S3 
crude, 267 
Gilsonite, 270 
liquid, 275 

specifications for, 275 
petroleum residue, 270 
properties of, 270 
binding power, 271 
chemical stability, 270 
freedom from decomposition, 271 
resiliency, 271 
waterproofness, 271 
refined, 267 
rock, 268 
shipping, 270 
sources, 268 

tests, see Bituminous materials, tests 
Trinidad, 268 
Asphalt pavement, 411 
amount in U. S., 320 
block, 470 

composition, 471 
cost, 472 
merits, 472 
concrete, 461, 464 
Amiesite, 462 
bitulithic, 461 

area in U. S., 320 
cost of construction, 465 
Amiesite, 467 
bitulithic, 467 
Topeka mixture, 465 
Warrenite, 467 
definition, 461 
laying, 464 
merits, 466 
mixing, 464 
specifications, 468 
stone-filled, 463 
Topeka mixture, 463 
Warrenite, 462 
foundation, 412 
bituminous, 413 
hydraulic, 412 
kinds, 411 

block, 411, 470 
concrete, 411, 461, 464 
Amiesite, 462 
bitulithic, 461 
stone-filled, 463 
Topeka mixture, 465 
Warrenite, 462 



of. 



ASP 

Asphalt pavement, kinds, rock, 469 
sheet, 411 
rock, 469 

construction, 469 
sheet, 411 

adjacent to track, 441 
binder course, 415 
bitumen, 417 
kind, 415 
closed, 415 

specifications, 416 
open, 415 

specifications, 415 
paint coat, 415 
laying, 419 
mixing, 418 
rolUng, 422 
thickness, 422 
cause of failure, 443 

improper manipulation, 444 
burned asphalt, 444 
chilled cement, 445 
damp foundation, 445 
high heat, 444 
improper consistency, 444 
inadequate compression, 446 
inadequate mixing, 445 
insufficient bitumen, 445 
rich binder, 445 

separation of sand and cement, 445 
natural causes, 446 
bonfires, 448 
cracks, 447 
decay, 446 
illuminating gas, 447 
leaky joints, 447 
ordinary wear, 446 
porous foundations, 446 
shifting under traffic, 448 
weak foundation, 446 
unsuitable materials, 443 
asphalt, 416, 417, 426 
sand, 416, 417, 423 
cost of construction, 451 
actual, 454 
estimated, 453 
cost of maintenance, 454 
contract, 457 

Buffalo, 458 
municipal plant, 455 
Brooklyn, 457 
crown, 46 
foundation, 412 
bituminous, 413 
hydraulic, 412 
other forms, 414 
grade, maximum, 459 
history, 412 

merits, 460 
repairing, method of, 449 
cracks, 450 
disintegration, 449 
formation of waves, 449 
old material, 451 
painting gutters, 450 
settlement of subgrade, 449 



659 




660 



INDEX 



ASP— BIT 

Asphalt pavement, sheet, repairs, method of 
recording, 450 
price of, 457, 458 
specifications, 460 
wearing coat, 423 

absorptive power, 433 
bitumen, per cent, 435 
cement, 426 
amount, 427 
testing, 427 

absorptive power, 433 
density, 432 
impact, 433 
density, 432 
filler, 426 
impact test, 433 
laying, 436 
mixing, 435 
proportions, 434 
rolling, 438 
sand, 423 
thickness, 441 

Bermudez asphalt, 269 

Bitulithic pavements, area in U. S., 320 

see also Asphalt pavements. 
Bitumen, 267 

Bituminous concrete roads, 310 
aggregate, 311 
binder, 311 
cost, 315 
laying, 312 
mixing, 311 
seal coat, 315 

vs. bituminous macadam, 315 
Bituminous macadam roads, 306 
applying binder, 309 
bituminous binder, 308 
characteristics, 310 
cost, 310 
crown, 307 
definition, 306 
foundation, 306 
maintenance, 310 
maximum grade, 307 
tar-sand mastic, 310 
wearing coat, 307 
width, 307 
Bituminous materials, 267 
definition, 267 
tests of, 271 

bitumen soluble in disulphide, 273 
naphtha, 273 
tetrachloride, 272 
consistency, 272 

float apparatus, 272 
penetration, 272 
viscosity, 272 
distillation, 273 
ductility, 274 
fixed carbon, 273 
flash point, 272 
float test, 272 
foam test, 271 
melting point, 272 
paraffin scale, 274 
penetration, 272 
specific gravity, 271 
vaporization, 273 
viscosity, 272 
Bituminous surface, definition, 296 
kinds, 296 
carpet, 298 

applying material, 299 
bituminous material, 298 
cleaning surface, 299 
cost, 303 

on gravel, 304 
on macadam, 304 
maintenance, 303 



BIT— BRI 

Bituminous surface, kinds, carpet, value of 
302 

coating, 297 

bituminous material, 297 
Blocks, size of city, 337 
Brick, 475 

chemical composition, 475 
clay, 475 
hillside, 480 
kinds, 478 

hillside, 482 

re-pressed, 478 

vertical fiber, 481 

wire-cut lug, 479 
manufacture, 476 

burning, 483 

cutting, 477 

moulding, 476 
re-pressed, 478 
service test, 500 
size, 485 

specifications, 485 
testing, 486 

absorption, 489 

appearance, 486 

color, 487 

crushing strength, 488 

rattler test, 490 

changes proposed, 499 
limit of loss, 495, 497, 499 
marking brick, 493 
specifications, 491 

size, 487 

specific gravity, 488 

transverse strength, 489 
vertical fiber, 481 
wire-cut lug, 479 
Brick pavements, 474 
adjacent to track, 539 
area in U. S., 320 
bedding course, 505 

cement and sand, 511 

mortar, 512 

sand cushion, 505 
comparison of types, 536 

cost, 539 

durability, 536 

noisiness, 536 

smoothness, 536 

thickness, 537 

time in construction, 539 
construction, 503 

bedding course, 505 
cement-sand, 511 
comparison, 514 
mortar, 512 
sand, 505 
cost, 544 

discussion, 544 

examples, 546-51 
expansion joint, 533 

at anchors, 535 

longitudinal, 533 

transverse, 534 
foundation, 503 

abandoned type, 503 

bituminous concrete, 504 

hydraulic concrete, 505 

macadam 504 
grade, maximum, 540 
header, 535 
inspecting, 519 
joint filler, 521 

applying, 524 

bituminous, 530 

cost, 529 

grout, 522 

merits, 529 

mixing, 523 

sand, 521 



INDEX 



661 



BRI— CON 


CON— DRA 




Brick pavements, joint filler, tar-sand, 532 


Concrete roads, portland cement, construc- 


laying brick, 514 


tion, curing, 252 




delivery, 514 


finishing, 251 




direction of courses, 515 


machine, 256 




rolling, 519 


mixing, 246 




setting, 517 


one vs. two course, 241 




maintenance, 552 


placing, 249 




cost, 564 


proportions, 245 




repairs, 552 


protecting, 252 




bulges, 557 


side forms, 244 




contraction joints, 555 


striking, 249 




cracks, 560 


thickness, 244 




defective grouting, 555 


width, 244 




longitudinal cracks, 557 


contraction joints, 254 




re-laying, 558 


cross section, 242 




re-surfacing, 561 


curbs, 258 




asphalt, 561 


data for estimates, 235 




brick, 563 


drainage, 238 




tar, 563 


grade, maximum, 243 




settlement of trench, 554 


maintenance, 264 




shrinkage of cushion, 553 


bituminous surface, 265 




sinking of foundation, 554 


cost, 265 




soft brick, 552 


work required, 264 




. transverse joints, 534 


materials, 227 




turning brick, 563 


aggregates, 228 




merits, 549 


cement, 227 




monolithic, 512 


gravel vs. broken stone, 229 




roads, 541 


one vs. two course, 241 




specifications, 551 


reinforcement, 256 




streets, 541 


shoulders, 257 




Brick rattler, 492 


specifications, 264 




specifications, 491 


subgrade, 239 




Bridges, 112 


super-elevation, 243 




Broken stone, see Macadam stone. 


template, 250 
thickness, 244 




Catch basins, 362 


width, 244 




construction, 362 


Connecticut gravel road, 170 




cover, 366 


Crown, pavements, 374 




examples, 363, 364, 365 


amount of, 275 




inlet, 366 


laying out, 374 




location, 364 


roads, 65 




Catch-water, 83 


Culverts, 113 




Cement, asphalt, 268 


Curb, 378 




hydraulic, 227 


combined, 382 




Census, travel, 25 


expansion joints, 386 




see also Travel census. 


finishing surface, 386 




Chevy Chase experimental brick road, 501 


forms, 383 




Clay-sand roads, see Sand-clay roads. 


foundation, 383 




Cobble-stone pavements, area in U. S., 320 


laying and mixing, 384 




construction, 567 


concrete, 380 




hammer, 568 


cost, 381 




Concrete, bituminous, see Bituminous con- 


integral, 258 




crete. 


stone, 378 




aggregate, 228 


cost, 380 




cement, 227 


Curves, horizontal, in road, 58 




consistency, 248 


vertical, at grade intersection, 353 




data for estimates, 235 


Cut-back product, definition, 267 




gravel, 229 






ingredients for cu. yd., 236 


Distance equivalent to 1 ft. of rise and fall 


54 


Fuller's rule, 237 


value of saving, 43 




materials, 227 


vs. rise and fall, 53 




aggregate, 228 


Drainage, road, 72 




cement, 227 


catch-waters, 83 




gravel, 229 


side ditches, 78 




stone, 229 


surface, 81 




methods of proportioning, 230 


crown, 82 




mixers, 247 


side ditches, deep, 82 




mixing, 246 


shallow, 82 




proportions, 245 


street, 361 




theory of, 230 


catch basins, 362 




sieve analysis, 231 


constructions, 362 




Concrete curb and gutter, 382 


examples, 363 




see also Curb. 


Champaign, 363 




Concrete pavements, 263 


Milwaukee, 365 




see also Concrete roads. 


London, 365 




Concrete roads, portland-cement, 227 


Providence, 364 




characteristics, 263 


inlet, 366 




construction, 238 


intersection, 370 




consistency, 248 


commercial, 369 




cost, 259 


Champaign, 368 





662 



INDEX 



DRA— EAR 

Drainage, street, catch basins, intersection, 
Omaha, 368 
location, 364 
crown, 374 

dished-pavements, 376 
foot-crossing, 372 
gutter, 367 
depth, 369 
grade, 370 
material, 367 
Dynagraph, 19 

Earth roads, 70 

artistic treatment, 114 
construction, 70 

earthwork, see Earthwork, 
machinery, see Road-building machinery, 
cross section, 71, 82, 83 

super-elevation, 71 
crown, 65, 81 
definition, 70 
drainage, 72 
surface, 81 

side ditches, 78, 82, 83, 84 
underdrainage, 72 
object, 72 
tile, 74 
cost, 75 
fall, 75 
laying, 77 
cost, 77 
location, 78 
size, 76 
earthwork, see Earthwork, 
embankments, rolling, 89 
settlement, 88 
stability, 90 
grades, 71 
improving old, 91 

machinery, see Road-building machinery, 
maintenance, 115 
care of ditches, 124 
surface, 117 
roadside, 124 
trees, 125 
cost, 129, 130 
dragging, 129 
total, 130 
destructive agents, 115 v 

equal axles, 117 
horse before wheel, 117 
narrow tires, 115 
dragging, 120 

cost of, 121, 129 
filling holes, 124 
improvin-g old roads, 91 
machinery, see Road-building machinery, 
preventing dust, 133 
removing stones, 124 
scraping, cost of, 123 
snow, obstruction by, 125 
systems, 126 

by contract, 129 
continuous maintenance, 127 
continuous repairs, 127 
intermittent repairs, 127 
V road-leveler, 123 
surface oiling, 133 
applying the oil, 135 
cost, 136 

effect on maintenance, 134 
oil, see Oil; also Petroleum, 
preparing surface, 135 
width, 70 

on curves, 71 
Earthwork, 83 

balancing cuts and fills, 86 
computing, 86 
cost of, 103 

drag-scoop scraper, 104 



EAR— GRA 

Earthwork, cost of, elevating grader, 104 

finishing slopes, ll2 

profits, 112 

scraper, four-wheel, 110 
two-wheel, 106 

scraping grader, 103 

wagons, 110 
embankment, rolling, 89 

settling, 88 

stability of, 90 
overhaul, 89 
rolling, 89 

setting slope stakes, 86 
settlement, 88 
shrinkage, 87 
Elevating grader, 101 

operating, 102 
Embankments, 85 
cross section, 85 
finishing slopes, 112 
rolling, 89 
settling, 88 
stability of, 90 
Excavation, 84 
cross section, 85 

Flux, 267 

specifications, 274 
Foot-way crossing, 372 
Foundation, pavements, 392 
bituminous concrete, 406 
concrete base, hydraulic cement, 399 
cost, 403 
curing, 403 
finishing, 402 
mixing, 402 
placing, 402 
proportions, 401 
thickness, 400 
drainage, 392 

see also Drainage, 
earthwork, 393 

see also Earthwork, 
filling trenches, 395 
flooding, 396 
natural settlement, 395 
re-filling with sand, 398 
replacing material, 398 
tamping, 397 
macadam, 405 
railway track, 407 

examples, 408 
subgrade, 392 
roUing, 394 
thickness, 400 
French coefficient of wear, 188 
French standard macadam road, 198, 199 

Grade, effect on load, 50 
effect on location, 48, 69 
maximum, 54 
minimum, 57 
Grade resistance, 21 
Grader, elevating, 101 
scraping, 95 
Shuart, 208 
Granite pavements, amount in U. S., 320 
Granite paving blocks, 574 
Gravel, road-building, 150 
binder, 151 

materials of, 151, 152, 153 
characteristics, 158 

Buck Hill, 160, 161, 163 
Decatur, 160, 161 
Lexington, 160, 161, 162 
Oaktown, 160, 161, 163 
Paducah, 160, 161, 164 
Peekskill, 160, 161, 162 
Rockford, 160, 161, 164 
Rock Hill, 160, 161, 163 



INDEX 



663 



GRA-HOR 

Gravel, road-building, characteristics, Ros- 
etta, 160, 161, 164 
Shaker Prairie, 160, 161, 163 
Shark River, 160, 161, 163 
Urbana, 159, 160, 161 
cherty, 155 
composition of, 158 
defined, 150 
distribution of, 154 
durability, 150 
exploring for, 156 
mineralogical analysis ofi 161 
requisites for, 150 
binder, 151 
durability, 150 
sizes, 151 
screening, 173 
sieve analysis, 160 
sizes, 151 
Gravel pavements, amount in U. S., 320 
Gravel roads, 150 

bituminous surface, see Bituminrus surface. 
Connecticut standard, 170 
construction, 165 
bottom course, 172 
Connecticut Standard, 170 
cost, 175 
cross section, 169 
crown, 166, 355 
drainage, 165 

forcing gravel into subgrade, 174 
forms of construction, 167 
comparisons of, 171 
surface, 167 
trench, 169 
hauling gravel, 174 
loading gravel, 174 
measuring gravel, 174 
rolling, 171 
specifications, 178 
durability, 178 
dust palliative, 181 

moistening with salts, 182 
practice in Washington, D. C, 183 
sprinkling with fresh water, 181 
light oil, 183, 192 
proprietary compounds, 182 
sea water, 181 
earth track beside, 171 
economic value, 176 
grade, maximum, 166 
maintenance, 178 
cost, 180 

destructive agents, 178 
re-surfacing, 180 
sprinkling, 180 
Texas standard, 170 
tractive resistance, 15, 16, 18, 21 
travel on, effect of, 177 
width, 166 
Guard rails, 113 
Guide posts, 114 
Gutter, 367, 381 
combined, 382 
concrete, 382 
cost, 388 

finishing surface, 386 
forms, 383 
foundation, 383 
laying, 384 
depth, 369 
expansion joint, 386 
grade, 370 
material, 367 
private driveway, 389 
street intersection, 370 

Hammer, brick, 519 

stone-block, 579 
Horse, power of, 22 



HOR— PAV 

Horse, power of, effect of grade upon, 23 
maximum load on grade, 24 

Iron ore, binder for gravel roads, 152 

Jarrah wood, description of, 603 

Karri wood, description of, 603 

Labor road tax, 38 
Load, effect of grade on, 23 
Location of roads, 41 
curves, 58 

aesthetic value, 61 

super-elevation, 60 
distance, 42 

value of saving, 41 
grade, 45 

effect of, 47 

limiting effect of, 50 

maximum, 54 

minimum, 57 

rise and fall, 47 

vs. distance, 53 
grade Une, 69 
placing line, 65 
safety at summit, 56 
wheelway, position of, 64 
width, 61 

improved portion, 62 

on curves, 64 

right-of-way, 61 
Lute for sand cushion, 508 

Macadam pavement, 634, 635 

area in U. S., 320 
Macadam road, 185 

see also Bituminous Macadam, 306 
Water-bound Macadam, 185 
Macadam stone, 186 
binding power, 186 
cementing power, 186 
hardness, 186 
tests of, 187 
abrasion, 188 
cementation, 188 
hardness, 187 
impact, 187 
toughness, 187 
toughness, 186 
Massachusetts standard macadam road, 197, 
198 

New Jersey standard macadam road, 197 
New York standard macadam road, 197 

Oil for roads, cost of, 288 
specifications for, 286 

earth roads, 287 

gravel roads, 287 

macadam roads, 287 

park drives, 286 
Oiling machines, 137 
Oil, see Petroleum. 
Over-haul, 89 

Pavement administration, 321 
causes of inefficiency, 322 
conditions, 321 
importance of problem, 321 
remedy, 324 
Pavements, apportionment of cost, 326, 328 
area of, in U. S., 320 
asphalt, see Asphalt pavements, 
assessments for, 329 

area rule, 330 

frontage rule, 330 

legality of levy, 331 

terms of payment, 331 
benefits, 318 



684 



INDEX 



PAV— ROA 

Pavements, brick, see Brick pavements, 
cobble-stone, see Cobble-stone pavements, 
comparisons, 642, 654 

cost of construction, 642, 656 
cost of maintenance, 643 
renewals, 645 
repairs, 643, 657 
sprinkling, 652 
total, 653 

transportation, 632 
comfort in use, 650 
durability, 635 

ease of cleaning, 648, 651, 657 
freedom from mud and dust, 650 
bealthfulness, 650 
noiselessness, 649 
slipperiness, 647 
temperature, 650 
tractive resistance, 646, 657 
concrete, see Concrete pavements. 
cross section, 355 

side-hill streets, 355 
crown, 355 
foundation, 392 

bituminous concrete, 406 
hydraulic concrete, 399 
macadam, 405 
gravel, see Gravel roads, 
guaranteeing, 331 

maintenance by contract, 333 
investments in, 319 
openings, 334 
selecting the best, 633 
stone-block, see Stone- block pavements, 
tearing up, 334 
widths of, 345 

with car tracks, 345 
without car tracks, S' 6 
wood-block, see Wood-tlock pavements. 
Pavement foundation, see Foundation. 
Paving railway areas, 407. 441, 539, 587, 623 
Petroleum, 283 

asphalt content, 285 
asphalt residue, 270 
classification, 283 
cost of, 288 

method of refining, 284 
shipping, 284 
specifications for, 286 
Poll tax, 35 
Preserving timber, see Wood-block pavement. 

Rails, car tracks, 409 
Railway rails, 409 
Railway ties, 409 
Rammer, brick, 520 

stone-block, 582 

wood-block, 617 
Rattler for testing brick, 492 

Specifications, 491 
Retaining walls, 113 
Road, artistic treatment, 114 

bituminous concrete, see Bituminous con- 
crete roads. 

bituminous surfaces for, see Bituminous sur- 
faces. 

earth, see Earth roads. 

gravel, see Gravel roads. 

hydraulic concrete, see Concrete roads. 

macadam, see Bituminous macadam roads. 
see Water-bound macadam roads. 

sand, see Sand roads. 

sand-clay, see Sand-clay roads. 

taxes, see Taxes. 
Road administration, 30 

national, 34 

state, 32 

unit, 31 
Roads, advantages of good, 3 

artistic treatment of, 114 



ROA- STO 

Roads, classification, 34 

estimated cost of bad, 10 

expenditures for in U. S., 40 

improving old, 91 

toll, 35 
Road-building machinery, 91 

drag, see Road drag 

elevating grader, 101 

roller, 212 
tandem, 213 
three-wheel, 212 

scrapers, 92, 93, 94 

scraping grader, 95 
Road drag, 117 

plank, 118 

rules for using, 120 

split-log, 118 

steel, 118 
Road grader, scraping, 95 

elevating, 101 
Road improvement, financial value of, 11 
Rollers, 213 

asphalt type, 213 

macadam type, 212 

tandem type, 213 

three-wheel type, 212 

Sand roads, 139 
drainage, 139 
hardening the surface, 13G 
shade, 139 

tractive resistance, 16, 21 
Sand-clay roads, 140 

clay on sand subgrade, 145 
clay, 145 
construction, 146 
cost, 147 
design, 141 
maintenance, 148 

natural mixtures of sand and clay, 141 
construction, 143 
tests of, 141 
. sand on clay subgrade, 143 
construction, 145 
proportions, 144 
sand, 144 
thickness, 144 
travel census of, 149 
Scrapers, 92 
drag, 92 
Fresno, 93 
scoop, 92 
slip, 92 
w^heel, 94 

four-wheel, 95 
two-wheel, 95 
Scraping grader, 95 

operating, 97 
Snow, cost of clearing, 126 

obstruction by, 125 
State aid, 32 

Stone-block hammer, 579 
Stone-block pavement, 566 
adjacent to track, 586 
amount in U. S., 320 
classification, 566 
Belgian block, 568 
cobble-stone, 567 
durax, 569 
oblong block, 568 
Roman, 566 
rubble, 568 
construction, 572 
beddinjg course, 572 
mortar, 574 
sand, 573 
blocks, 574 
dressing, 574 

re-cutting, 576 
measu^-ing, 577 



INDEX 



665 



STO— STR 

Stone-block pavement, construction, blocks, 
ramming, 580 
settin^g, 579 
size, 577 

re-cutting, 576 
filling joints, 582 
asphalt, 585 
gravel, 582 
grout, 586 
pea gravel, 582 
tar and sand, 584 
foundation, 572 
cost, 591 
blocks, 591 
Buffalo, 595 
Chicago, 592 
Cleveland, 597 
contract price, 598 
durax, 593 
grouting, 593 

Medina stone, 595, 596, 597 
New York, 593 
re-cutting and re-laying, 592 
Rochester, 597 
Schenectady, 573 
tar-sand filler, 596 
various cities, 598 
dujax, 588 
expansion joint, 587 
grade, maximum, 587 
granite, 569 
hammer, 579 
limestone, 572 
maintenance, 597 
cost, 599 

raising blocks, 599 
re-filling joints, 599 
re-laying, 598 
repairs, 598 

settlement of trenches, 599 
sinking of foundation, 599 
spalling joints, 599 
Medina sandstone, 571 
merits, 588 
paver's hammer, 579 
paver's rammer, 520, 582 
quartzite, 572 
sandstone, 571 
Colorado, 571 
Kettle River, 572 
Medina, 571 
Potsdam, 571 
Sioux Falls, 572 
trap, 571 
Stone-block rammer, 582 
Stone crusher, 203 
gyratory, 204 
oscillatory, 203 
Stone-crushing plant, 205 
Street, cross section on side-hill, 355 
design, 336 

area of streets, 344 
blocks, size of, 337 
location of streets, 339 
directness, 341 
topography, 339 
plan of streets, 336 
blocks, size of, 337 
lots, size of, 337 
shade trees, 338 
width of streets, 343 
drainage, see Drainage, street, 
grades, 347 

elevations at street intersection, 350 
maximum, 348 
minimum, 349 

vertical curves at intersection, 353 
location, 339 
directness, 341 
topography, 339 



STR— VEH 

Street, pavements, width of, 343 

with car tracks, 346 

without car tracks, 345 
plan of streets, 336 

checker-board, 341 

concentric, 343 

diagonal, 341 
trees, 358 

vertical curves, 354 
width, 343 
Swiss standard macadam road, 198 

Tar, 289 

characteristics, 289 

cost of, 295 

kinds, 289 

shipping, 290 

specifications, 289 

bituminous concrete, 292 
bituminous macadam, 291 
bituminous surfaces, 291 
filler for block pavements, 294 
trade names, 294 

tests of, see Bituminous materials, tests of. 

trade names, 294 
Tax, road, 34 

automobile, 40 

labor, 38 

money, 38 

poll, 35 

property, 38 

toll, 35 
Telford road, 185, 189, 191 
Template, brick pavements, 505, 513 
mortar bedding-course, 513 
sand cushion, 505 
concrete roads, 249 
Texas gravel road, 170 
Thank-you-marms, 83 
Ties, street-railway, 409 
Tile, cost of, 75 

drainage, 72 

laying, 77 

location, 78 

one vs. two lines, 77 

size of, 76 

weight, 75 
Tires, width of, effect on traction, 14 
Tractive resistance, 12 

American experiments, 19 

axle friction, 12 

data on, 15, 16, 17, 18, 20, 21 

diameter of wheel, effect of, 13 

French experiments, 17 

rolling resistance, 13 

speed, effect of, 16 

springs, effect of, 17 

width of tire, effect of, 14 
Transportation, cost of wagon, 6 

annual saving, 10 
Travel census, 25 

American roads, 26 
streets, 28 

classification of travel, 28 
diverting travel, 29 
weight of vehicles, 29 

French, 26 

history, 26 

Illinois, 27 

Iowa, 28 

Massachusetts, 26 

weight of vehicles, 30 

width of traveled way, 29 

width of vehicles, 31 
Trees on street, 358 
Trinidad asphalt, 268 

V road-leveler, 123 
Vehicles, weight of, 30 
width of, 30 



666 



INDEX 



WAS— WOO 

Washington, sprinkling gravel with oil, 183 

street plan of, 342 
Water-bound macadam, 185 
binder, 216 

bituminous surface, see Bituminous sur- 
faces, 
construction, 189 
binding, 217 
cost, 220 
crown, 192 
foundation, 189 
rolling, 213 
setting Telford, 201 
shoulders, 191 
shrinkage, 209 
size of stone, 204 
spreading stone, 207 
subgrade, 190, 200 
super-elevation, 194 
Telford's, 191 
thickness, 194 
Ts-idth, 191 
wings, 196 
crown, 192 
crushing stone, 202 
grade, permissible, 199 
maintenance, 223 
cost, 226 
forms of, 189 
patching, 225 
raveling, 224 
rolling, 226 
sprinkling, 226 
standard, French, 198, 199 
Massachusetts, 197, 198 
New Jersey, 191, 197 
New York, 197 
Swiss, 198 
super-elevation, 194 
thickness, 194 
width, 191 
wings, 196 
Water-breaks, 83 
Water-ways, 113 
Wheelway, position of, 64 

width of, 62 
Wings for macadam roads, 196 
Wood-block pavement, 601 
adjacent to track, 623 
area in U. S., 320 
blocks, 604 

care after treatment, 611 
causes of decay, 605 
laying, 615 
specifications, 604 
dimensions, 604 



WOO 

Wood-block pavement, blocks, specifications 
quality, 605 
testing, 611 
treatment, 609 
construction, 612 
bedding course, 612 
bituminous, 614 
mortar, 613 
sand, 612 
cost, 623 
blocks, 623 
examples, 625 
various cities, 627 
filling joints, 618 
grout, 618 
sand, 618 
tar, 618 
foundation, 612 
laying blocks, 615 
crown, 623 
decay, cause of, 605 
expansion joints, 622 
grade, maximum, 623 
history, 602 
kinds, 601 

rectangular blocks, 602 
round blocks, 601 
maintenance, 628 
bleeding, 630 
bulges, 630 
cost, 631 
low spots, 629 
poor blocks, 628 
re-laying, 630 
merits, 626 
open joints, 621 
preservative, 605 
amount, 611 
specifications, 607 
creosote oil, 607 
coal-tar distillate, 607 
coal-tar pa%'ing oil, 608 
water-gas tar, 608 
rolling, 617 
specifications, 604 
treatment, 609 

open-tank process, 609 
pressure process, 609 
timber, 603 
hemlock, 604 
jarrah, 603 
karri, 603 
larch, 604 
pine, 604 
tamarack, 604 
yellow pine, 603 



'I 












u.'Vy 

















'IS 



